Filling liquid

ABSTRACT

In a droplet ejection apparatus for forming a conductive pattern with a conductive pattern formation ink comprised of a water-based dispersion medium and metal particles dispersed in the water-based dispersion medium by an ink jet method, the droplet ejection apparatus includes a droplet ejection head having a reservoir with ink chambers for storing the conductive pattern formation ink and a plurality of nozzles from which droplets of the conductive pattern formation ink are to be ejected by the ink jet method. A filling liquid is used instead of the conductive pattern formation ink for filling the reservoir and the ink chambers to prevent the reservoir and the ink chambers from being dried when the droplet ejection apparatus is not used for a certain period of time. The filing liquid is comprised of the water-based dispersion medium, a sugar alcohol A and a surfactant A. The filling liquid can be easily and reliably replaced with the conductive pattern formation ink.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims a priority to Japanese Patent Application No. 2007-319025 filed on Dec. 10, 2007 which is hereby expressly incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present invention relates to a filling liquid, and more specially relates to a filling liquid used for filling a reservoir and ink chambers formed in a droplet ejection head of a droplet ejection apparatus when the droplet ejection apparatus is not used for a certain period of time.

2. Related Art

A ceramic circuit substrate including a substrate (ceramic substrate) formed of a ceramic material and a wiring formed of a metal material and provided on the substrate has been widely used as a circuit substrate (wiring substrate) on which electronic parts are to be mounted.

In such a ceramic circuit substrate, the substrate (ceramic substrate) itself is formed of a multifunctional material such as the ceramic material. Therefore, there are merits in that if the ceramic circuit substrate is formed into a multilayer substrate having a plurality of ceramic layers, inner layer parts can be formed easily between the ceramic layers, and in that the ceramic circuit substrate can be produced with high dimensional accuracy.

The above ceramic circuit substrate can be produced by applying a composition containing metal particles onto a ceramic molded body made of a material containing ceramic particles and a binder in a predetermined pattern corresponding to that of a wiring (conductive pattern) to be formed, and then subjecting the ceramic molded body on which the composition has been applied to a degreasing treatment and a sintering treatment.

A screen printing method has been widely used as a method of forming a pattern on such a ceramic molded body. On the other hand, recently, miniaturization of the wiring (having a line width of 60 μm or less) and reduction of pitches between the wirings are required for densification of the circuit substrate.

However, use of the screen printing method has a disadvantage for miniaturization of the wiring and reduction of pitches between the wirings. As a result, it is difficult to respond to the above requirements by the screen printing method due to the disadvantage.

For this reason, recently, as an alternative method of forming a pattern on the ceramic molded body, there has been proposed use of what is called an ink jet method, i.e., a liquid droplet ejection method by which a liquid material (conductive pattern formation ink) containing metal particles is ejected in the form of liquid droplets from nozzles of a liquid droplet ejection head, (see, e.g., JP-A-2007-84387). By using such an ink jet method, it is possible to satisfy both demands of miniaturization of the wiring and reduction of pitches between the wirings.

In the meantime, a reservoir and ink chambers (hereinafter, simply referred to as “ink flow path” in the Related Art) formed in a droplet ejection apparatus (droplet ejection head) used in forming a conductive pattern are generally filled with water for the purpose of preventing dry of the inside thereof when the droplet ejection apparatus is not used for a certain period of time.

In the case where the droplet ejection head is operated again, the water filled into the ink flow path is replaced with or substituted for a conductive pattern formation ink. As a result, the conductive pattern formation ink can be ejected from nozzles of droplet ejection head. However, in the case where water is used as the filling liquid, there are problems as follows.

First, in a state that water is filled in the ink flow path, the inside of the ink flow path is prevented from drying. However, since an inner surface of the ink flow path has low affinity to water, there is a case that the inside (inner surface) of the ink flow path (in particular, the vicinity of ejection portions of the droplet ejection head) is dried during a time after water is removed from the ink flow path and before the conductive pattern formation ink is filled therein.

If the inner surface of the ink flow path is dried in this way, air bubbles are allowed to enter into the ink flow path so that conductive pattern formation ink can not be ejected stably. As a result, there is a problem in that ejection stability is reduced.

Further, since water has high surface tension, it is difficult to fill the entire of the ink flow path with the water completely. That is to say, some portions of the ink flow path may remain in a state that they are not filled with the water. As a result, there is a high risk that the conductive pattern formation ink can not be ejected stably due to dry at the portions of the ink flow path.

Furthermore, even if water is removed from the ink flow path, water partially remains in the ink flow path due to the high surface tension. In such a case, the remaining water is mixed with the conductive pattern formation ink during filling thereof.

In the meantime, a surfactant is normally contained in a conductive pattern formation ink for obtaining high dispersibility of metal particles contained therein. As described above, in the case where water partially remaining in the ink flow path is mixed with the conductive pattern formation ink, concentration of the surfactant is decreased in the portions of the ink flow path in which the partially remaining water is mixed with the conductive pattern formation ink.

As a result, dispersibility of the metal particles is partially reduced in the portions of the ink flow path, thereby generating aggregates of the metal particles. As a result, there is a case that the conductive pattern formation ink can be not ejected stably.

Furthermore, there may be conseived that the conductive pattern formation ink is filled into the ink flow path while discharging water by the conductive pattern formation ink instead of removing the water from the ink flow path.

However, according to this method, in the vicinity of a boundary between water and the conductive pattern formation ink in the ink flow path, concentration of the surfactant contained in the conductive pattern formation ink is partially decreased as described above. This may also causes the case that the conductive pattern formation ink can not be ejected stably.

SUMMARY

It is an object of the present invention to provide a filling liquid which can be easily and reliably replaced with a conductive pattern formation ink.

In order to achieve the object, a first aspect of the present invention is directed to in a droplet ejection apparatus for forming a conductive pattern with a conductive pattern formation ink comprised of a water-based dispersion medium and metal particles dispersed in the water-based dispersion medium by an ink jet method, the droplet ejection apparatus including a droplet ejection head having a reservoir with ink chambers for storing the conductive pattern formation ink and a plurality of nozzles from which droplets of the conductive pattern formation ink are to be ejected by the ink jet method, wherein a filling liquid is used instead of the conductive pattern formation ink for filling the reservoir and the ink chambers to prevent the reservoir and the ink chambers from being dried when the droplet ejection apparatus is not used for a certain period of time, wherein the filing liquid is comprised of the water-based dispersion medium, a sugar alcohol A and a surfactant A.

This makes it possible to provide a filling liquid which can be easily replaced with the conductive pattern formation ink.

In the present invention described above, it is preferred that the conductive pattern formation ink further comprises a sugar alcohol B, wherein the sugar alcohol A contained in the filling liquid includes the same kind of sugar alcohol as a kind of the sugar alcohol B contained in the conductive pattern formation ink.

This makes it possible to prevent ejection portions of the droplet ejection head from being dried and provide a filling liquid which can be more easily and reliably replaced with the conductive pattern formation ink.

In the present invention described above, it is also preferred that the conductive pattern formation ink further comprises a surfactant B, and the surfactant B is constituted of components, wherein the surfactant A contained in the filling liquid includes at least a part of the components constituting the surfactant B contained in the conductive pattern formation ink.

This makes it possible to prevent dispersibility of the metal particles contained in the conductive pattern formation ink from being lowered when replacing the filling liquid with the conductive pattern formation ink.

In the present invention described above, it is also preferred that the sugar alcohol A includes at least one of xylitol and sorbitol.

This makes it possible to effectively prevent ejection portions of the droplet ejection head from being dried and provide a filling liquid which can be more easily and reliably replaced with the conductive pattern formation ink.

In the present invention described above, it is also preferred that an amount of the sugar alcohol A contained in the filling liquid is in the range of 3 to 25 wt %.

This makes it possible to effectively prevent ejection portions of the droplet ejection head from being dried and provide a filling liquid which can be more easily and reliably replaced with the conductive pattern formation ink.

In the present invention described above, it is also preferred that a hydrophile lipophile balance (HLB) of the surfactant A is in the range of 8 to 16.

This makes it possible to improve affinities of the inner surfaces of the reservoir and the ink chambers formed in the droplet ejection head to the conductive pattern formation ink, thereby enabling to easily fill the conductive pattern formation ink therein.

In the present invention described above, it is also preferred that the surfactant A includes an acetylene glycol-based compound.

This makes it possible to improve affinities of the inner surfaces of the reservoir and the ink chambers formed in the droplet ejection head to the conductive pattern formation ink, thereby enabling to easily fill the conductive pattern formation ink therein.

In the present invention described above, it is also preferred that the acetylene glycol-based compound has an acetylene group, and a bilateral symmetry structure in which the acetylene group is placed at the center.

This makes it possible to improve affinities of the inner surfaces of the reservoir and the ink chambers formed in the droplet ejection head to the conductive pattern formation ink with a small additive amount thereof, thereby enabling to easily fill the conductive pattern formation ink therein.

In the present invention described above, it is also preferred that an amount of the surfactant A contained in the filling liquid is in the range of 0.05 to 5 wt %.

This also makes it possible to effectively improve affinities of the inner surfaces of the reservoir and the ink chambers formed in the droplet ejection head to the conductive pattern formation ink with a small additive amount thereof, thereby enabling to easily fill the conductive pattern formation ink therein.

In the present invention described above, it is also preferred that the filling liquid further comprises hydroxyl acid or a salt of the hydroxyl acid having three or more COOH and OH groups in total, wherein a number of the COOH groups is equal to or greater than a number of the OH group(s).

This also makes it possible to improve affinities of the inner surfaces of the reservoir and the ink chambers formed in the droplet ejection head to the conductive pattern formation ink with a small additive amount thereof, thereby enabling to easily fill the conductive pattern formation ink therein.

In the present invention described above, it is also preferred that the filling liquid further comprises mercapto acid or a salt of the mercapto acid having two or more COOH and SH groups in total.

This also makes it possible to improve affinities of the inner surfaces of the reservoir and the ink chambers formed in the droplet ejection head to the conductive pattern formation ink with a small additive amount thereof, thereby enabling to easily fill the conductive pattern formation ink therein.

In the present invention described above, it is also preferred that surface tension of the filling liquid is in the range of 20 to 50 dyn/cm, wherein the surface tension of the filling liquid is equal to or smaller than surface tension of the conductive pattern formation ink.

This makes it possible to easily fill a filling liquid into the reservoir and the ink chambers formed in the droplet ejection head. Further, it is also possible to improve affinities of the inner surfaces of the reservoir and the ink chambers formed in the droplet ejection head to the conductive pattern formation ink with a small additive amount thereof, thereby enabling to easily fill the conductive pattern formation ink therein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a schematic configuration of an ink jet apparatus.

FIG. 2 is a pattern diagram for explaining a schematic configuration of an ink jet head.

FIG. 3 is a longitudinal section view showing one example of a wiring substrate according to the present invention, that is, a ceramic circuit substrate.

FIG. 4 is an explanatory view schematically illustrating steps of a method of producing the wiring substrate shown in FIG. 3, that is, the ceramic circuit substrate.

FIGS. 5A and 5B are views for explaining a production process of the wiring substrate shown in FIG. 3, that is, the ceramic circuit substrate.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Filling Liquid

A filling liquid according to the present invention is filled into a reservoir 95 and ink chambers 93 (hereinafter, simply referred to as an “ink flow path”) formed in a droplet ejection head 70 of a droplet ejection apparatus 50 when the droplet ejection apparatus 50 is not used for a certain period of time, is stored (preserved) for a certain period of time, or is carried.

The filling liquid has a function of a storage liquid by being filled into the ink flow path formed in the droplet ejection head 70 of the droplet ejection apparatus 50 in which a conductive pattern formation ink 10 as described later (hereinafter, simply referred to as “ink 10”) is ejected from the ejection portions (nozzles) 91.

In the meantime, a reservoir and ink chambers (hereinafter, simply referred to as “ink flow path” in the Related Art) formed in a droplet ejection apparatus (droplet ejection head) used in forming a conductive pattern are generally filled with water for the purpose of preventing dry of the inside thereof when the droplet ejection apparatus is not used for a certain period of time.

In the case where the droplet ejection head is operated again, the water filled into the ink flow path is replaced with or substituted for a conductive pattern formation ink. As a result, the conductive pattern formation ink can be ejected from nozzles of droplet ejection head. However, in the case where water is used as the filling liquid, there are problems as follows.

First, in a state that water is filled in the ink flow path, the inside of the ink flow path is prevented from drying. However, since an inner surface of the ink flow path has low affinity to water, there is a case that the inside (inner surface) of the ink flow path (in particular, the vicinity of ejection portions of the droplet ejection head) is dried during a time after water is removed from the ink flow path and before the conductive pattern formation ink is filled therein.

If the inner surface of the ink flow path is dried in this way, air bubbles are allowed to enter into the ink flow path so that conductive pattern formation ink can not be ejected stably. As a result, there is a problem in that ejection stability is reduced.

Further, since water has high surface tension, it is difficult to fill the entire of the ink flow path with the water completely. That is to say, some portions of the ink flow path may remain in a state that they are not filled with the water. As a result, there is a high risk that the conductive pattern formation ink can not be ejected stably due to dry at the portions of the ink flow path.

Furthermore, even if water is removed from the ink flow path, water partially remains in the ink flow path due to the high surface tension. In such a case, the remaining water is mixed with the conductive pattern formation ink during filling thereof.

In the meantime, a surfactant is normally contained in a conductive pattern formation ink for obtaining high dispersibility of metal particles contained therein. As described above, in the case where water partially remaining in the ink flow path is mixed with the conductive pattern formation ink, concentration of the surfactant is decreased in the portions of the ink flow path in which the partially remaining water is mixed with the conductive pattern formation ink.

As a result, dispersibility of the metal particles is partially reduced in the portions of the ink flow path, thereby generating aggregates of the metal particles. As a result, there is a case that the conductive pattern formation ink can be not ejected stably.

Furthermore, there may be conceived that the conductive pattern formation ink is filled into the ink flow path while discharging water by the conductive pattern formation ink instead of removing the water from the ink flow path. However, according to this method, in the vicinity of a boundary between water and the conductive pattern formation ink in the ink flow path, concentration of the surfactant contained in the conductive pattern formation ink is partially decreased as described above. This may also causes the case that the conductive pattern formation ink can not be ejected stably.

Under such circumstances, a present inventor has studied strenuously. As a result, it has been confirmed that the problems described above can be solved by using a filling liquid which contains a water-based dispersion medium and a sugar alcohol and a surfactant dispersing (dissolving) in the water-based dispersion medium as a filling liquid to be filled into an ink flow path of a droplet ejection head of a droplet ejection apparatus.

The filling liquid according to the present invention contains the water-based dispersion medium, the sugar alcohol A and the surfactant A. In this way, since the filling liquid contains the surfactant A, it is possible to improve affinity of an inner surface of the ink flow path formed in the droplet ejection head 70 to the filling liquid. This is supposed to result from reasons as follows.

When the filling liquid is filled into the ink flow path, high affinity between the filling liquid and the inner surface of the ink flow path can be obtained due to inclusion of the surfactant A in the filling liquid. Due to this high affinity, a film constituted of the filling liquid is formed on the inner surface of the ink flow path.

Therefore, even if the filling liquid is removed from the ink flow path formed in the droplet ejection head 70, since the film constituted of the filling liquid is formed on the inner surface of the ink flow path, it is possible to obtain affinity of the film to the ink 10.

Such an affinity of the film formed on the inner surface of the ink flow path to the ink 10 makes it possible to prevent air bubbles from being entered into the ink flow path when filling the ink 10 into the ink flow path. As a result, it is possible to easily fill the ink 10 into the ink flow path.

In the case where the filling liquid is replaced with (substituted for) the ink 10 and filled into the ink flow path, even if the ink 10 is partially mixed with the filling liquid in the ink flow path, it is possible to prevent concentration of the surfactant A contained therein from being extremely decreased.

Therefore, it is possible to prevent the metal particles from being partially aggregated. As a result, it is possible to stably eject the ink 10 filled into the ink flow path from ejection portions 91 of the droplet ejection head 70.

Further, inclusion of the sugar alcohol A in the filling liquid makes it possible to effectively prevent the vicinity of the ejection portions 91 of the droplet ejection head 70 from being dried during preservation or rest of the droplet ejection head 70. Additionally, the inclusion makes it possible to rapidly mix or replace the filling liquid with the ink 10.

Furthermore, inclusion of the sugar alcohol A in the filling liquid makes it possible to prevent or suppress the film constituted of the filling liquid, which is formed on the inner surface of the ink flow path as described above, from being dried.

Therefore, even if the filling liquid has been removed from the ink flow path, it is possible to maintain affinity of film formed on the inner surface of the ink flow path to the ink 10 for a relatively long period of time so that the ink 10 can be easily filled into the ink flow path.

Since such a filling liquid is easily replaced with the ink 10, it is possible to easily remove the filling liquid filled into the ink flow path by using the ink 10.

In contrast, if the filling liquid does not contain the surfactant A, effects as described above can not be sufficiently obtained. In other words, in the case where a filling liquid containing no surfactant A is used, there is a case that it is impossible to improve affinity of the inner surface of the ink flow path to the ink 10, thereby entering air bubbles into the ink flow path when filling the ink 10 into the ink flow path. As a result, there is a case that the ink 10 can not be ejected stably.

Generally, an ink contains a surfactant (dispersant). Therefore, when the ink is mixed with the filling liquid containing no surfactant, of which a small amount remains in the ink flow path after discharging the filling liquid, in the ink flow path, concentration of the surfactant contained in the ink 10 is decreased in a mixture of the ink 10 and the filling liquid.

This makes it possible to lower dispersibility of the metal particles in the mixture so that aggregates of the metal particles, adherences of the metal particles to the inner surface of the ink flow path, or the like is generated with ease. As a result, there is also a case that the ink 10 can not be ejected stably.

On the other hand, if the filling liquid does not contain the sugar alcohol A, effects as described above can not be sufficiently obtained. In other words, in the case where a filling liquid containing no sugar alcohol A is used, after the filling liquid is removed from the ink flow path formed in the droplet ejection head 70, the ink flow path, namely the inner surface thereof is dried immediately. Therefore, there is a possibility that air bubbles are mixed into the ink or entered into the ink flow path when filling the ink 10 into the ink flow path.

Under such circumstances, in the case where an ink containing a sugar alcohol B as a drying suppressant as described later is used, there are problems as follows. After the filling liquid containing no sugar alcohol A has been removed from the ink flow path, the ink containing the sugar alcohol B is filled into the ink flow path. In this regard, a small amount of the filling liquid remains in the ink flow path.

In this case, the filling liquid remaining in the ink flow path is mixed with the filled ink to obtain a mixture, so that concentration of the sugar alcohol B which has been contained in the ink is decreased in the mixture. In this way, when the concentration of the sugar alcohol B which has been contained in the ink is decreased, the metal particles are separated out the vicinity of the ejection portions 91 of the droplet ejection head 70 due to volatilization of the water-based dispersion medium contained in the ink. As a result, clogging of the ejection portions 91 or the like occurs.

Hereinafter, a description will be made on components constituting the filling liquid.

Water-Based Dispersion Medium

First, a description will be made on the water-based dispersion medium. In this embodiment, the term “water-based dispersion medium” means a liquid constituted of water and/or a liquid having good compatibility with water (that is, a liquid having solubility of 30 g or higher with respect to water of 100 g at 25° C.).

As described above, the water-based dispersion medium is constituted of water and/or a liquid having good compatibility with water, but it is preferred that the water-based dispersion medium is mainly constituted of water. In this regard, an amount of the water contained in the water-based dispersion medium is preferably 70 wt % or more, and more preferably 90 wt % or more.

Further, it is preferred that a composition of the water-based dispersion medium contained in the filling liquid is the substantially same as that of a water-based dispersion medium constituting the ink 10 described later. This makes it possible to easily and reliability replace (substitute) the filling liquid filled into the ink flow path with (for) the ink 10.

Examples of such a water-based dispersion medium include water; an alcohol-based solvent such as methanol, ethanol, butanol, propanol, isopropano, ethylene glycol or propane diol; an ether-based solvent such as 1,4-dioxane or tetrahydrofuran (THF); an aromatic heterocyclic compound-based solvent such as pyridine, pyrazine or pyrrole; an amide-based solvent such as N,N-dimethylformamide (DMF) or N,N-dimethylacetamide (DMA); a nitrile-based solvent such as acetonitrile; an aldehyde-based solvent such as acetaldehyde; and the like. These materials may be used singly or in combination of two or more of them.

Further, an amount of the water-based dispersion medium contained in the filling liquid is preferably in the range of 65 to 95 wt % and more preferably in the range of 75 to 85 wt %. This makes it possible to reliably adjust a viscosity of the filling liquid, thereby obtaining high characteristics of the filling liquid.

Sugar Alcohol A

The sugar alcohol A contained in the filling liquid has a function of preventing the vicinity of the ejection portions 91 of the droplet ejection head 70 from being dried. Further, the sugar alcohol A also has a function of preventing the ink flow path (inner surface thereof) from drying after the filling liquid has been removed from the ink flow path before the ink 10 filled into the ink flow path.

This makes it possible to prevent air bubbles from being mixed into the ink or entered into ink flow path when filling the ink 10 into the ink flow path. Further, it is possible to easily and reliability replace the filling liquid with the ink 10.

Further, examples of the sugar alcohol A include glycerin, threitol, erythritol, pentaerythritol, dipentaerythritol, tripentaerythritol, arabitol, ribitol, xylitol, sorbitol, mannitol, gulitol, talitol, galactitol, allitol, altritol, dolucitol, iditol, glycerin (glycerol), inositol, maltitol, isomaltitol, lactitol, turanitol and the like. These sugar alcohols may be used singly or in combination of two or more of them.

Among the sugar alcohol A mentioned above, the sugar alcohol A is preferably xylitol and/or sorbitol. This makes it possible to effectively prevent the ink flow path from being dried, thereby enabling to easily replace the filling liquid with the ink 10. Further, it is also possible to easily fill the ink 10 into the ink flow path.

In the case where xylitol and/or sorbitol are/is used as the sugar alcohol A, it is preferred that the filling liquid contains at least one of maltitol and lactitol.

Both xylitol and sorbitol are components having a superior effect that dry of ink flow path or the inner surface thereof can be prevented. However, these components also have property that they are easily crystallized. Therefore, by containing the at least one of maltitol and lactitol in addition to xylitol and/or sorbitol in the filling liquid, it is possible to effectively prevent xylitol and/or sorbitol from being crystallized and separated out from the ink 10. Further, it is also possible to effectively prevent the ink flow path from being dried.

It is preferred that the sugar alcohol A contained in the filling liquid includes the same kind of sugar alcohol as that of sugar alcohol B contained in the ink 10 as described later. This makes it possible to easily and reliability replace the filling liquid with the ink 10 due to the same kind of sugar alcohol. As a result, the ink 10 can be easily and reliability filled into the ink flow path.

An amount of the sugar alcohol A contained in the filling liquid is preferably in the range of 3 to 25 wt % and more preferably in the range of 5 to 20 wt %. This makes it possible to effectively prevent the ink flow path from being dried and easily and effectively replace the filling liquid with the ink 10 in the ink flow path. As a result, the ink 10 can be easily filled into the ink flow path.

Surfactant A

As described above, the surfactant A is contained in the filling liquid according to the present invention. This makes it possible to improve affinity of the inner surface of the ink flow path formed in the droplet ejection head 70 to the ink 10. Therefore, it is possible to prevent air bubbles from being entered into the ink flow path when the ink 10 is filled into the ink flow path.

As a result, the ink 10 can be stably ejected from the ejection portions 91 of the droplet ejection head 70. Further, it is also possible to easily replace the filling liquid with the ink 10 so that the ink 10 can be easily filled into the ink flow path.

The surfactant A contained in the filling liquid is not particularly limited to a specific material, but it is preferred that the surfactant A contains at least one part of components constituting a surfactant B which is contained in the ink 10 described later. This makes it possible to easily replace the filling liquid with the ink 10 so that the ink 10 can be more easily filled into the ink flow path.

Additionally, even if a small amount of the filling liquid remains in the ink flow path when the ink 10 has been replaced with the filling liquid in the ink flow path formed in the droplet ejection head 70, it is possible to prevent or suppress characteristics such as a viscosity of the ink 10 and the like from being changed.

As described above, the surfactant A to be used to the filling liquid is not particularly limited a specific material, but it is preferred that the surfactant A includes an acetylene glycol-based compound. This makes it possible to more easily replace the filling liquid with the ink 10.

Further, it is possible to effectively improve affinity of the inner surface of the ink flow path formed in the droplet ejection head 70 to the ink 10. Therefore, it is possible to more reliably prevent air bubbles from being entered into the ink flow path when the ink 10 is filled into the ink flow path.

Furthermore, it is preferred that the acetylene glycol-based compound has a bilateral symmetry structure in which an acetylene group thereof is placed at the center. This makes it possible to effectively improve affinity of the inner surface of the ink flow path formed in the droplet ejection head 70 to the ink 10 with a small additive amount thereof.

Examples of the acetylene glycol-based compound include SURFYNOL 104 series (e.g., 104E, 104H, 104PG-50, 104PA), SURFYNOL 400 series (e.g., 420, 465, 485), OLFINE series (e.g., EXP4036, EXP4001, E1010) and the like. Here, “SURFYNOL” and “OLFINE” are product names of Nissin Chemical Industry Co., Ltd. These acetylene glycol-based compounds may be used singly or in combination of two or more of them.

A hydrophile lipophile balance (HLB) of such a surfactant A contained in the filling liquid is preferably in the range of 8 to 16 and more preferably in the range of 9 to 14. This makes it possible to reliably improve affinity of the inner surface of the ink flow path formed in the droplet ejection head 70 to the ink 10. As a result, it is possible to easily fill the ink 10 into the ink flow path.

Further, an amount of the surfactant A contained in the filling liquid is preferably in the range of 0.05 to 5 wt % and more preferably in the range of 0.5 to 2 wt %. This makes it possible to more efficiently improve affinity of the inner surface of the ink flow path formed in the droplet ejection head 70 to the ink 10. As a result, it is possible to easily fill the ink 10 into the ink flow path.

Other Components

Further, compounds other than the components described above may be contained in the filling liquid.

Examples of such compounds include a hydroxy acid or a salt thereof having three or more COOH and OH groups in total, wherein the number of the COOH groups is equal to or greater than the number of the OH group(s). Such compounds are components which are easily adsorbed to surfaces of the metal particles contained in the filling liquid, and thereby improving affinity of the inner surface of the ink flow path to the ink 10.

This makes it possible to prevent air bubbles from being entered into the ink flow path when the ink 10 is filled into the ink flow path. Further, it is also possible to more easily fill the ink 10 into the ink flow path.

Examples of such compounds include citric acid, malic acid, trisodium citrate, tripotassium citrate, trilithium citrate, triammonium citrate, disodium malate, tannic acid, gallo tannic acid, Gallo tannin and the like. These compounds may be used singly or in combination of two or more of them.

Further, it is preferred that compounds other than the compounds mentioned above include a mercapto acid or a salt thereof having two or more COOH and SH groups in total. Such compounds are components which are easily adsorbed to surfaces of the metal particles contained in the filling liquid, and thereby improving affinity of the inner surface of the ink flow path to the ink 10.

This makes it possible to prevent air bubbles from being entered into the ink flow path when the ink 10 is filled into the ink flow path. Further, it is also possible to more easily fill the ink 10 into the ink flow path.

Examples of such compounds include mercaptoacetic acid, mercaptopropionic acid, thiodipropionic acid, mercaptosuccinic acid, thioacetic acid, sodium mercaptoacetate, sodium mercaptopropionate, sodium thiodipropionate, disodium mercaptosuccinate, potassium mercaptoacate, potassium mercaptopropionate, potassium thiodipropionate, dipotassium mercaptosuccinate, and the like. These compounds may be used singly or in combination of two or more of them.

It is preferred that surface tension at a temperature of 25° C. of the filling liquid as described above is smaller than that of the ink 10. This makes it possible to reliably fill the filling liquid into the ink flow path formed in the droplet ejection head 70 during filling of the filling liquid to the ink flow path. Therefore, it becomes difficult for air bubbles to enter into the ink flow path.

The surface tension at the temperature of 25° C. of the filling liquid is not particularly limited to a specific value, but is preferably in the range of 20 to 50 dyn/cm and more preferably in the range of 20 to 40 dyn/cm. This makes it possible to reliably fill the filling liquid into the ink flow path formed in the droplet ejection head 70 during filling of the filling liquid to the ink flow path.

Further, even if a small amount of the filling liquid remains in the ink flow path, it is possible to reduce adverse effects which may occur due to high surface tension of the ink 10 as described later. In this regard, it is to be noted that the surface tension can be used a value which is measured according to JIS K 3662 in this specification.

Hereinafter, a description will be made on the ink 10 (conductive pattern formation ink) which is reliably replaced with the filling liquid in the ink flow path as described above.

Conductive Pattern Formation Ink (Ink)

The ink 10 which is reliably replaced with (substituted for) the filling liquid in the ink flow path as described above is an ink for forming a conductive pattern on a base member and, more specifically, an ink for forming the conductive pattern on the base member by using a droplet ejecting method.

The base member on which the conductive pattern is to be formed may be constituted of any kind of material, but is preferably a ceramic substrate mainly constituted of ceramic in this embodiment. Further, in this embodiment, it is described that the ink 10 is supplied to sheet-like ceramic green body (ceramic green sheet 7) constituted of a material which contains ceramics and a binder.

In this regard, it is to be noted that the ceramic green body and the ink 10 supplied thereto are subjected to a sintering treatment as described later to obtain the ceramic substrate and the conductive pattern, respectively.

Hereinafter, a description will be made on a preferred embodiment of the ink 10 which is reliably replaced with the filling liquid according to the present invention in the ink flow path. In this embodiment, a description will be representatively offered regarding a case that a dispersion solution (ink) including silver particles (metal particles) dispersed therein is used as a dispersion solution in which metal particles are dispersed in a water-based dispersion medium.

The ink 10 of this embodiment is constituted of a water-based dispersion medium, silver particles dispersed in the water-based dispersion medium, a polyglycerin compound having a polyglycerin skeleton, a sugar alcohol B and a surfactant B.

Water-Based Dispersion Medium

First, a description will be made on the water-based dispersion medium. The water-based dispersion medium is used the substantially same compositions as those of the water-based dispersion medium constituting the filling liquid as described above. This makes it possible to easily replace the ink 10 with the filling liquid, thereby enabling to easily fill the ink 10 into the ink flow path.

An amount of the water-based dispersion medium contained in the ink 10 is preferably in the range of 25 to 60 wt % and more preferably in the range of 30 to 50 wt %. This makes it possible to reliably adjust a viscosity of the ink 10 so that it is possible to prevent or suppress the viscosity of the ink 10 from being changed by volatilization of the water-based dispersion medium.

Silver Particles

Next, a description will be made on the silver particles (metal particles). The silver particles are a main component of the conductive pattern to be formed on the ceramic substrate and a causal component of conductive property in the conductive pattern.

The silver particles disperse in the ink 10. An average particle size of the silver particles is preferably in the range of 1 to 100 nm and more preferably in the range of 10 to 30 nm. This makes it possible to obtain an ink 10 which can be ejected more stably from the ejection portions 91 of the droplet ejection head 70, and to form a conductive pattern having a fine pattern with ease.

Further, an amount of the silver particles (which do not adsorb the dispersant described later) contained in the ink 10 is in the range of 0.5 to 60 wt % and more preferably in the range of 10 to 45 wt %. This makes it possible to more effectively prevent disconnection of the conductive pattern. Therefore, it is possible to provide a conductive pattern having higher reliability.

Furthermore, it is preferred that the silver particles (metal particles) are dispersed in the water-based dispersion medium as silver colloid particles in which a dispersant is adsorbed to surfaces of the silver particles. This makes it possible to obtain superior dispersibility of the silver particles in the water-based dispersion medium. Therefore, it is possible to reliably improve ejection property of the ink 10.

It is preferred that the dispersant is formed of a hydroxy acid or a salt thereof having three or more COOH and OH groups in total, wherein the number of the COOH groups is equal to or greater than the number of the OH group(s). The dispersant is adsorbed to surfaces of the silver particles to form the silver colloid particles.

The dispersant acts to stabilize a colloid solution by allowing the silver colloid particles to be uniformly dispersed in the water-based dispersion medium (colloid solution) under electrical repulsion forces of the COOH groups present in the dispersant.

In this way, stable present of the silver colloid particles in the ink 10 makes it possible to more easily form a conductive miniaturization pattern. Further, in the pattern (pre-pattern) formed by using such an ink 10, the silver particles are distributed uniformly so that cracks, disconnections of wires or the like occur difficulty.

In the contrast, if the total of the COOH and OH groups contained in the dispersant is less than three, or if the number of the COOH groups is smaller than the number of the OH groups, there is a case that dispersibility of the silver colloid particles cannot be obtained sufficiently.

Examples of such a dispersant include citric acid, malic acid, trisodium citrate, tripotassium citrate, trilithium citrate, triammonium citrate, disodium malate, tannic acid, Gallo tannic acid, Gallo tannin and the like. These materials may be used singly or in combination of two or more of them.

Further, mercapto acid or a salt thereof having two or more COOH and SH groups in total may be contained in the dispersant. The dispersant is adsorbed to surfaces of the silver particles through mercapto groups thereof to form the silver colloid particles.

The dispersant also acts to stabilize the colloid solution by allowing the silver colloid particles to be uniformly dispersed in the water-based dispersion medium (colloid solution) under electrical repulsion forces of the COOH groups present in the dispersant.

In this way, stable present of the silver colloid particles in the ink 10 makes it possible to more easily form a conductive miniaturization pattern. Further, in the pattern (pre-pattern) formed by using such an ink 10, the silver particles are distributed uniformly so that cracks, disconnections of wires or the like occur difficulty.

In contrast, if the total of the COOH and SH groups contained in the dispersant is less than two, that is, one of the COOH and SH groups is contained in the dispersant, there is a case that dispersibility of the silver colloid particles cannot be obtained sufficiently.

Examples of such a dispersant include mercaptoacetic acid, mercaptopropionic acid, thiodipropionic acid, mercaptosuccinic acid, thioacetic acid, sodium mercaptoacetate, sodium mercaptopropionate, sodium thiodipropionate, disodium mercaptosuccinate, potassium mercaptoacate, potassium mercaptopropionate, potassium thiodipropionate, dipotassium mercaptosuccinate, and the like. These materials may be used singly or in combination of two or more of them.

An amount of the silver colloid particles contained in the ink 10 (colloid solution) is in the range of about 1 to 60 wt % and more preferably in the range of about 10 to 50 wt %. If the amount of the silver colloid particles falls below the lower limit value noted above, an absolute amount of the silver contained in the ink 10 becomes too small. As a result, there is a need to apply the ink 10 several times when the conductive pattern is formed into a relatively thick film.

In contrast, if the amount of the silver colloid particles exceeds the upper limit value noted above, the amount of the silver colloid particles contained in the ink 10 becomes too great unnecessarily, thus lowering dispersibility of the silver colloid particles. In order to avoid the dispersibility reduction, it is necessary to increase frequency of stirring the ink 10.

When the silver colloid particles is heated up to 500° C. in a thermogravimetric analysis, a heat loss of the silver colloid particles is preferably in the range of about 1 to 25 wt %. As the silver colloid particles (solid contents) is heated up to 500° C., the dispersant adsorbed to the surfaces of the silver particles and the reducing agent (residual reducing agent) described below are oxidatively decomposed and are gasified and eliminated for their most parts.

Since a quantity of the residual reducing agent seems to be insignificant, it may be conceived that the loss of the silver colloid particles when heated up to 500° C. corresponds substantially to a quantity of the dispersant present in the silver colloid particles.

If the loss-on-heating is smaller than 1 wt %, the quantity of the dispersant relative to that of the silver particles becomes too small, thus lowering dispersibility of the silver colloid particles. In contrast, if the loss-on-heating is greater than 25 wt %, a quantity of a residual dispersant relative to that of the silver particles becomes too great, consequently increasing specific resistance of the conductive pattern.

The specific resistance can be improved to a certain degree by heating and sintering the conductive pattern after formation thereof to decompose and eliminate organic components. Therefore, it is preferred that the ink 10 of the present invention is used for forming the conductive pattern on a substrate which is sintered at a higher temperature, such as a ceramic substrate.

In this regard, it is to be noted that a method of producing the silver colloid particles will be described below in detail.

Sugar Alcohol B

A sugar alcohol B is contained in the ink 10. The sugar alcohol B has superior moisture-retaining property and can prevent volatilization of the water-based dispersion medium contained in the ink 10. In other words, the sugar alcohol B serves as a drying suppressant.

Therefore, inclusion of the sugar alcohol B in the ink 10 makes it possible to prevent the dispersant contained in the ink 10 from being volatilized during preservation or storage for a predetermined period of time, thereby preventing increase of the viscosity of the ink 10. Therefore, the ink 10 can be stably ejected from the ejection portions 91 of the droplet ejection head 70 for a long period of time.

Further, when stopping an ejecting operation of the droplet ejection apparatus 50 or ejecting the ink 10 continuously for a long period of time, it is possible to prevent or suppress the water-based dispersion liquid from being volatilized in the vicinity of the ejection portions 91 of the droplet ejection head 70, thereby enabling to stably eject the ink 10 from the ejection portions (nozzles) 91 of the droplet ejection head 70. As a result, a conductive pattern having high reliability can be easily formed in a predetermined shape.

Further, when a patterned formed by using the ink 10, that is, a pre-pattern before being transformed (changed) into the conductive pattern is dried (namely, the water-based dispersion medium is removed from the pre-pattern), a concentration of the sugar alcohol B in the pre-pattern is increased due to the evaporation of the water-based dispersion medium therefrom.

This makes it possible to increase a viscosity of the ink 10 constituting the pre-pattern. Therefore, it is possible to more reliably prevent the ink 10 from diffusing toward an undesired region on the base member. As a result, a conductive pattern having a desired shape can be formed on the base member with high accuracy.

The sugar alcohol B contained in the ink 10 is not particularly limited a specific material. Examples of such a sugar alcohol B include the same alcohols as included in the sugar alcohol A as described above. Among the alcohols mentioned above, since xylitol and sorbitol exhibit a superior function as the drying suppressant, they can be reliably used as a component of the ink 10.

Further, in the case where at least one of maltitol and lactitol in addition to xylitol and/or sorbitol is used to the ink 10, it is possible to effectively prevent xylitol and/or sorbitol from being crystallized.

An amount X (B) of the sugar alcohol B with respect to the silver particles of 100 parts by weight is preferably in the range of 4 to 55 parts by weight and more preferably in the range of 5 to 35 parts by weight in the ink 10.

This makes it possible to reliably prevent the water-based dispersion liquid contained in the ink 10 from being evaporated. Therefore, it is possible to stably eject droplets of the ink 10 from the ejection portions (nozzles) 91 of the droplet ejection head 70 for a long period of time.

An amount of the sugar alcohol B contained in the ink 10 is preferably in the range of 1 to 15 wt % and more preferably in the range of 2 to 10 wt %. This makes it possible to reliably prevent the water-based dispersion liquid contained in the ink 10 from being evaporated. Therefore, it is possible to stably eject droplets of the ink 10 from the ejection portions 91 of the droplet ejection head 70 for a long period of time.

In contrast, if the amount of the sugar alcohol B contained in the ink 10 is lower than the lower limit value noted above, there is a case that moisture-retaining property of the ink 10 (colloid solution) cannot be obtained sufficiently.

On the other hand, in the case where the amount of the sugar alcohol B contained in the ink 10 exceeds the upper limit value noted above, the amount of the sugar alcohol B becomes excessively large as compared with that of the silver particles (silver colloid particles).

This causes increase of specific resistance of the conductive pattern. In this regard, the specific resistance of the conductive pattern can be improved to a certain degree, by controlling sintering conditions such as a sintering time and a sintering atmosphere.

Further, since the sugar alcohol B is rapidly decomposed and removed at a predetermined temperature, there is a case that cracks generate in the conductive pattern due to rapid volumetric shrink age depending on a sintering temperature condition. As a result, there is also a case that this causes breaking conduction of the conductive pattern.

Polyglycerin Compound

The polyglycerin compound has a function of preventing generation of cracks in the patterned film (that is, the pre-pattern described later) formed by using the ink 10 when drying the patterned film (namely, when removing the water-based dispersion medium from the pre-pattern).

This function is conceived as follows. Inclusion of such a polyglycerin compound in the ink 10 ensures that polymer chains exist between the silver particles (metal particles). This makes it possible to maintain an adequate distance between the silver particles.

Further, the polyglycerin compound has a relatively high boiling point. Therefore, the polyglycerin compound is not removed during evaporation (removing) of the water-based dispersion medium, but is absorbed to the surfaces of the silver particles.

In addition, the polyglycerin compound continues to exist around the silver colloid particles for a long period of time, thereby avoiding any rapid volumetric shrink age of the pre-pattern of the conductive pattern and any grain growth of the silver particles when removing the water-based dispersion medium from the pre-pattern.

When the pre-pattern is sintered for forming the conductive pattern, the polyglycerin compound can prevent disconnections of wires from occurring. This effect is conceived as follows.

The polyglycerin compound has a relatively high boiling point or decomposition temperature. In a process of forming the conductive pattern with the ink 10, the polyglycerin compound can be evaporated or oxidatively decomposed after the water-based dispersion medium contained in the ink 10 (colloid solution) has been evaporated.

In the case where the pre-pattern is sintered for forming the conductive pattern, before the polyglycerin compound is evaporated or oxidatively decomposed, the polyglycerin compound exists around the silver particles and can prevent them from approaching and aggregating together. On the other hand, after the polyglycerin compound is decomposed, the silver particles can be fused so that they can be bond uniformly since the silver particles uniformly exist in the pre-pattern.

In the sintering process, the polymer chains of polyglycerin compound exist between the silver particles (metal particles) in the pre-pattern. This makes it possible to maintain an adequate distance between the silver particles. Further, the polyglycerin compound has appropriate fluidity.

Therefore, by containing the polyglycerin compound in the ink 10, even if a ceramics compact (particularly, a ceramic green sheet 7 which will be set forth below) is expanded and contracted by a temperature change thereof, the pre-pattern of the conductive pattern is also expanded and contracted following the ceramics compact. For the reasons stated above, it is conceived that it is possible to prevent disconnections in the formed conductive pattern from occurring.

The polyglycerin compound has a function of preventing the sugar alcohol B described above form being crystallized. Therefore, even if the ink 10 contains the sugar alcohol B, it is possible to prevent the sugar alcohol B form being crystallized in the conductive pattern formation process. Therefore, it is possible to prevent the formed conductive pattern from being damaged.

This is because since the sugar alcohol B and the polyglycerin compound have high affinity each other due to many hydroxyl groups in chemical structures thereof, the polyglycerin compound can enter between molecules of the sugar alcohol B, thereby preventing the sugar alcohol B from being crystallized.

Further, the polyglycerin compound has the high affinity to the sugar alcohol B described above. In addition, the sugar alcohol B has a relatively small molecular weight. Therefore, the sugar alcohol B enters into the molecular chains of the polyglycerin compound in the sintering process. Therefore, even if the water-based dispersion liquid is removed (evaporated) from the pre-pattern, high fluidity of the polyglycerin compound can be maintained.

As a result, it is possible to prevent cracks and disconnections from generating in the pre-pattern in the sintering process, thereby enabling to obtain the conductive pattern having high reliability. In other words, when the conductive pattern is formed by sintering the pre-pattern, the pre-pattern is contracted due to heat in the sintering process. However, even in such a case, since the pre-pattern has predetermined fluidity, it is possible to prevent cracks and disconnections from generating in the formed conductive pattern.

Further, the ceramics compact on which the pre-pattern is formed is also expanded and contracted in the sintering process. However, since the pre-pattern has predetermined fluidity, it is possible to prevent the cracks and the disconnections from generating in the formed conductive pattern.

Furthermore, inclusion of such a polyglycerin compound to the ink 10 makes it possible to appropriately adjust a viscosity of the ink 10, so that it is possible to effectively and stably eject the ink 10 from the ejection portions 91 of the droplet ejection head 70. Further, such an ink 10 can also exhibit increased film-forming capability.

Examples of such a polyglycerin compound include a polyglycerin compound having a polyglycerin chemical structure such as polyglycerin or polyglycerin ester, polyethylene glycol, and the like, one or more of which may be used independently or in combination.

Examples of the polyglycerin ester include polyglycerin monostearate, polyglycerin tristearate, polyglycerin tetrastearate, polyglycerin monooleate, polyglycerin pentaoleate, polyglycerin monolaurate, polyglycerin monocaprylate, polyglycerin polycyanurate, polyglycerin sesquistearate, polyglycerin decaoleate, polyglycerin sesquioleate, and the like.

Among the compounds stated above, it is preferable to use polyglycerin. This makes it possible to more reliably prevent generation of cracks and disconnections and also to reliably prevent crystallization of the sugar alcohol B. Further, polyglycerin is reliably used to the ink 10 due to high solubility to the water-based dispersion medium (water).

A weight average molecular weight of the polyglycerin compound used herein is preferably in the range of 300 to 3000 and more preferably in the range of 400 to 600. This makes it possible to more reliably prevent generation of cracks when drying the pre-pattern of the conductive pattern (that is, the pattered film formed of the conductive pattern formation ink).

Further, it is possible to prevent the sugar alcohol B from being crystallized in the conductive pattern formation process. Furthermore, it is possible to obtain high affinity between the polyglycerin compound and the sugar alcohol B. Therefore, the pre-pattern formed by using the ink 10 can be maintained fluidity thereof for a long period of time during the sintering process.

As a result, even if the ceramics compact (particularly, a ceramic green sheet 7 which will be set forth below) is expanded and contracted by a temperature change, the pre-pattern of the conductive pattern is also reliably expanded and contracted following the ceramics compact.

In contrast, if the weight average molecular weight of the polyglycerin compound is smaller than the lower limit value noted above, the polyglycerin compound tends to be decomposed during removing of the water-based dispersion medium, which in turn reduces the effect of preventing generation of cracks and crystallizations of the sugar alcohol B.

On the other hand, if the weight average molecular weight of the polyglycerin compound exceeds the upper limit value noted above, dispersibility and solbility of the silver colloid particles in the ink 10 (colloid solution) is lowered by an excluded volume effect of the polyglycerin compound or the like 10.

An amount of the polyglycerin compound contained in the ink 10 (colloid solution) is preferably in the range of 5 to 20 wt % and more preferably in the range of 6 to 19 wt %. This makes it possible to more effectively prevent generation of cracks.

In contrast, if the amount of the a polyglycerin compound is smaller than the lower limit value noted above, the effect of preventing generation of cracks is reduced in the case where the weight average molecular weight thereof falls below the lower limit value noted above.

On the other hand, if the amount of the polyglycerin compound is greater than the upper limit value noted above, dispersibility of the polyglycerin compound in the ink 10 (colloid solution) is lowered in the case where the weight average molecular weight thereof exceeds the upper limit value noted above. Therefore, there is a case that it is difficult to sufficiently reduce the viscosity of the ink 10.

Surfactant B

The ink 10 may contain a surfactant B in addition to the above components. The surfactant B has a function of improving dispersibility of the metal particles.

The surfactant B contained in the ink 10 is not particularly limited a specific material, but is preferably an acetyleneglycol-based compound.

The acetyleneglycol-based compound has a function of improving the dispersibility of the metal particles in the ink 10 and adjusting a contact angle of the ink 10 against the ceramics compact to a predetermined range. In other words, the acetyleneglycol-based compound is preferred because it can adjust the contact angle of the ink 10 against the ceramics compact to the predetermined range with a small additive amount.

Furthermore, in the case where the ink 10 contains such an acetyleneglycol-based compound, even if air bubbles are generated (contaminated) into ejected droplets of the ink 10, they can be rapidly removed from the ejected droplets of the ink 10. As described above, by adjusting the contact angle of the ink 10 against the ceramics compact to the predetermined range, it is possible to form a finer conductive pattern.

Specifically, by using the acetyleneglycol-based compound, the contact angle of the ink 10 against the ceramics compact is adjusted preferably to the range of 40 to 80° and more preferably to the range of 50 to 80°. If the contact angle is very small, there is a fear that a conductive pattern having a fine line width cannot be formed.

On the other hand, if the contact angle is very large, there is a fear that a conductive pattern having an even line width cannot be formed depending on ejection conditions of the ink 10 or the like. Further, when the droplets of the ink 10 are landed on the ceramics compact, a contact area therebetween becomes very small. As a result, there is a case that the landed droplets of the ink 10 slip from its landed point.

Further, it is preferred that the acetyleneglycol-based compound has a bilateral symmetry structure in which an acetylene group thereof is placed at the center. This makes it possible to adjust the contact angle of the ink 10 against the ceramics compact to the predetermined range with a small additive amount.

Examples of such an acetyleneglycol-based compound include SURFYNOL 104 series (e.g., 104E, 104H, 104PG-50, 104PA), SURFYNOL 400 series (e.g., 420, 465, 485), OLFINE series (e.g., EXP4036, EXP4001, E1010) and the like. These materials may be used singly or in combination of two or more of them. Here, “SURFYNOL” and “OLFINE” are product names of Nissin Chemical Industry Co., Ltd.

It is preferred that the ink 10 contains two or more kinds of acetyleneglycol-based compounds each having a different HLB value. This makes it possible to easily adjust the contact angle of the ink 10 against the ceramics compact to the predetermined range.

Especially, in the two or more kinds of the acetyleneglycol-based compounds, a HLB value difference between an acetyleneglycol-based compound having a highest HLB value and an acetyleneglycol-based compound having a lowest HLB value is preferably in the range of 4 to 12 and more preferably in the range of 5 to 10. This makes it possible to adjust the contact angle of the ink 10 against the ceramics compact to the predetermined range with smaller additive amounts of the acetyleneglycol-based compounds (that is, a surface tension adjuster).

In the case where the ink 10 containing the two or more kinds of the acetyleneglycol-based compounds is used, a HLB value of the acetyleneglycol-based compound having a highest HLB value is preferably in the range of 8 to 16 and more preferably in the range of 9 to 14. On the other hand, in this case, a HLB value of the acetyleneglycol-based compound having a lowest HLB value is preferably in the range of 2 to 7 and more preferably in the range of 3 to 5.

An amount of the acetyleneglycol-based compound contained in the ink 10 (colloid solution) is preferably in the range of 0.001 to 1 wt % and more preferably in the range of 0.01 to 0.5 wt %. This makes it possible to more effectively adjust the contact angle of the ink 10 against the ceramics compact to the predetermined range.

Other Components

The ink 10 may contain components other than the above components. For example, the ink 10 may contain polyalcohol such as polyethylene glycol, 1,3-butylene glycol, 1,3-propane diol, propylene glycol and the like.

Examples of the polyethylene glycol include polyethylene glycol #200 (having a weight average molecular weight of 200), polyethylene glycol #300 (having a weight average molecular weight of 300), polyethylene glycol #400 (having a weight average molecular weight of 400), polyethylene glycol #600 (having a weight average molecular weight of 600), polyethylene glycol #1000 (having a weight average molecular weight of 1000), polyethylene glycol #1500 (having a weight average molecular weight of 1500), polyethylene glycol #1540 (having a weight average molecular weight of 1540), polyethylene glycol #2000 (having a weight average molecular weight of 2000), and the like. These polyethylene glycols may be used singly or in combination of two or more of them.

Droplet Ejection Apparatus

Next, a description will be made on one example of a droplet ejection apparatus of which the ink flow path is filled by the filling liquid according to the present invention.

In this embodiment, ejection (application) of the ink 10 on the ceramic green sheet 7 by an ink jet method can be performed using, for example, an ink jet apparatus (droplet ejecting apparatus) 50 shown in FIG. 1, and an ink jet head (droplet ejection head) 70 shown in FIG. 2. Hereinafter, the ink jet apparatus 50 and the ink jet head 70 will be described in detail.

FIG. 1 is a perspective view showing the ink jet apparatus 50. Referring to FIG. 1, the left-and-right direction of a base 52 is designated by a X direction, the back-and-forth direction is designated by a Y direction, and the vertical direction is designated by a Z direction.

The ink jet apparatus 50 includes the ink jet head 70 (hereinafter simply referred to as “a head 70”) and a table 46 for supporting a substrate S (the ceramic green sheet 7 in this embodiment). An operation of the ink jet apparatus 50 is controlled by means of a control unit 53.

The table 46 for supporting the substrate S can be moved and positioned in the Y direction by means of a first moving means 54 and can be swung and positioned in a Oz direction by means of a motor 44.

On the other hand, the head 70 can be moved and positioned in the X direction by means of a second moving means (not shown) and can be moved and positioned in the Z direction by means of a linear motor 62. Furthermore, the head 70 can be swung and positioned in α, β and γ directions by means of motors 64, 66 and 68, respectively.

Based on this configuration, the ink jet apparatus 50 is capable of accurately controlling a relative position and posture between an ink ejecting surface 70P of the head 70 and the substrate S placed on the table 46.

A rubber heater (not shown) is arranged on a rear surface of the table 46. An upper whole surface of the ceramic green sheet 7 placed on the table 46 is heated up to a specified temperature by means of the rubber heater.

As shown in FIG. 2, the head 70 is designed to eject the ink 10 from ejection portions 91 according to an ink jet system (droplet ejection system).

The liquid droplet ejecting system may be any technique known in the art, including a piezo system in which the ink is ejected using a piezo element made of a piezoelectric body and a bubble system in which the ink is ejected using the bubbles generated when heating the ink.

Among them, the piezo system is advantageous in that it does not heat the ink 10 and therefore does not affect a composition of materials used. For this reason, the head 70 shown in FIG. 2 employs the piezo system.

The head 70 includes a head main body 90 having a reservoir 95 formed therein and a plurality of ink chambers 93 branched from the reservoir 95. The reservoir 95 serves as a flow path through which the ink 10 is supplied to the respective ink chambers 93.

A nozzle plate (not shown) that constitutes an ink ejecting surface is mounted to a lower end surface of the head main body 90. A plurality of nozzles 91 for ejecting the ink 10 are provided in the nozzle plate in a corresponding relationship with the respective ink chambers 93. An ink flow path is formed to extend from the reservoir 95 toward the corresponding nozzles 91 through the respective ink chambers 93.

On the other hand, a vibration plate 94 is mounted to an upper end surface of the head main body 90. The vibration plate 94 constitutes wall surfaces of the respective ink chambers 93. Piezo elements 92 are provided outside the vibration plate 94 in a corresponding relationship with the respective ink chambers 93.

The piezo elements 92 are formed of a piezoelectric material such as quartz or the like and a pair of electrodes (not shown) for holding the piezoelectric material therebetween. The electrodes are connected to a driving circuit 99.

If an electrical signal is inputted to the piezo elements 92 from the driving circuit 99, the piezo elements 92 undergo dilation deformation or shrink age deformation. As the piezo elements 92 undergo shrink age deformation, pressures of the ink chambers 93 are decreased and the ink 10 is admitted into the ink chambers 93 from the reservoir 95.

As the piezo elements 92 undergo dilation deformation, the pressures of the ink chambers 93 are increased and the ink 10 is ejected from the nozzles 91. A deformation amount of the piezo elements 92 can be controlled by changing a voltage applied thereto.

Furthermore, a deformation speed of the piezo elements 92 can be controlled by changing a frequency of thea voltage applied thereto. In other words, ejection conditions of the ink 10 can be controlled by adjusting conditions of a voltage applied to the piezo elements 92.

Accordingly, use of the ink jet apparatus 50 having the head 70 stated above makes it possible to accurately eject and deliver the ink 10 to a desired place in a desired quantity.

When the ink jet apparatus 50 (ink jet head 70) described above is not used for a long period of time, or the ink jet apparatus 50 (ink jet head 70) is preserved or transported, it is possible to prevent the inner surface (inside) of the ink flow path (reservoir 95 and ink chambers 93) from being dried by filling the filling liquid according to the present invention as described above.

Method of Producing Conductive Pattern Formation Ink

Next, one example of a method of producing the above conductive pattern formation ink (ink) will be described.

In the present embodiment, the ink 10 will be described as a colloid solution which contains silver particles dispersing in a water-based dispersion medium.

As described above, the ink 10 is comprised of the colloid solution containing the silver colloid particles in which the dispersant is adsorbed on surfaces of the silver particles. In this embodiment, the colloid solution is obtained by preparing an aqueous solution in which the dispersant and a reducing agent are dissolved, and then dropping an aqueous silver salt solution into the aqueous solution.

When the aqueous silver salt solution is dropped into the aqueous solution, Ag⁺ ions derived from a silver salt contained in the aqueous silver salt solution are reduced by the reducing agent contained in the aqueous solution, so that the Ag⁺ ions are transformed into silver atoms to produce the silver particles in the aqueous solution. Therefore, in this embodiment, the silver salt is a starting material for producing the silver particles.

In the method of producing the ink 10 of this embodiment, first, the aqueous solution in which the above dispersant and reducing agent are dissolved is prepared.

The dispersant is blended preferably in such a blending quantity that a mole ratio of the dispersant to silver contained in the silver salt becomes equal to about 1:1 to 1:100. Examples of the silver salt, which is the starting material of the silver particles, include silver nitrate and the like.

If the mole ratio of the dispersant to the silver salt becomes greater, a particle size of the silver particles grows smaller and contact points between the silver particles are increased. This makes it possible to obtain a conductive pattern whose volume resistance value is low.

As described above, the reducing agent acts to generate the silver particles through a reduction of Ag⁺ ions contained in the silver salt (starting material) such as the silver nitrate (Ag⁺NO³⁻) or the like.

The reducing agent is not particularly limited to a specific type. Examples of the reducing agent include: an amine-based reducing agent such as hydrazine, dimethylaminoethanol, methyldiethanolamine or triethanolamine; a hydrogen compound-based reducing agent such as sodium boron hydroxide, a hydrogen gas or hydrogen iodide; an oxide-based reducing agent such as carbon monoxide, sulfurous acid or hypophosphorous acid; a low-valent metal salt-based reducing agent such as a Fe (II) compound or a Sn (II) compound; an organic compound-based reducing agent such as sugar (e.g., D-glucose) or formaldehyde; a hydroxy acid, cited above as the dispersant, such as citric acid, malic acid or tannic acid; a hydroxy acid salt, cited above as the dispersant, such as trisodium citrate, tripotassium citrate, trilithium citrate, triammonium citrate or disodium malate; and the like. Among them, the hydroxy acid (including the tannic acid) or the salt thereof serves as both the reducing agent and the dispersant.

Further, the mercapto acid or the salt thereof, cited above as the dispersant, is preferably used as the reducing agent. This is because the mercapto acid or the salt thereof can be bonded to surfaces of the silver particles (metal particles) stably.

Examples of the mercapto acid include mercaptoacetic acid, mercaptopropionic acid, thiodipropionic acid, mercaptosuccinic acid and thioacetic acid. On the other hand, examples of the mercapto acid salt include sodium mercaptoacetate, sodium mercaptopropionate, sodium thiodipropionate, disodium mercaptosuccinate, potassium mercaptoacate, potassium mercaptopropionate, potassium thiodipropionate and dipotassium mercaptosuccinate.

These reducing agents and dispersants may be used independently or in combination. When using these compounds, it may be possible to accelerate a reducing reaction by applying light or heat thereto.

The reducing agent is blended in such a blending quantity as to completely reduce the silver salt which is the starting material of the silver particles. If the blending quantity is excessive, the reducing agent remains in the colloid solution (aqueous silver colloid solution) as impurities, which may be a cause of adversely affecting conductivity of the formed conductive pattern.

This means that the blending quantity should preferably be a smallest possible quantity. More specifically, the blending quantity is such that a mole ratio of the silver salt to the reducing agent becomes equal to about 1:1 to 1:3.

In this embodiment, it is preferred that, after the aqueous solution is prepared by dissolving the dispersant and the reducing agent in the solvent, pH of the aqueous solution is adjusted to 6 to 12.

The reason is as follows. For example, in the case of mixing the trisodium citrate as the dispersant and ferrous sulfate as the reducing agent, the pH of the aqueous solution becomes equal to about 4 to 5 depending on an overall concentration thereof, which falls below the pH 6 mentioned above.

At this time, equilibrium of a reaction represented by the following reaction equation (1) is shifted to the right side by hydrogen ions existing in the aqueous solution, thereby increasing a quantity of the COOH groups.

—COO⁻+H⁺→—COOH   (1)

This reduces electrical repulsion forces of the surfaces of the silver particles obtained by subsequently dropping the aqueous silver salt solution, which leads to reduction in dispersibility of the silver particles (colloid particles).

For this reason, after the aqueous solution has been prepared by dissolving the dispersant and the reducing agent in the solvent, an alkaline compound is added to the aqueous solution to reduce a hydrogen ion concentration thereof.

The alkaline compound added at this time is not particularly limited to a specific type. Examples of the alkaline compound include sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonia water and the like. Among them, it is preferable to use the sodium hydroxide that can easily adjust the pH with a small amount.

In this regard, addition of the alkaline compound in a quantity great enough to increase the pH of the aqueous solution to more than 10 is undesirable, because the hydroxide of ions of a residual reducing agent (that is, residue of the reducing agent) such as iron ions or the like is apt to precipitate.

Next, in the method of producing the ink 10 of this embodiment, the aqueous silver salt solution containing the silver salt is dropped into the aqueous solution in which the dispersant and the reducing agent are dissolved.

The silver salt is not particularly limited to a specific type. Examples of the silver salt include silver acetate, silver carbonate, silver oxide, silver sulfate, silver nitrite, silver chlorate, silver sulfide, silver chromate, silver nitrate, silver dichromate and the like. Among them, it is preferable to use the silver nitrate that exhibits high water-solubility.

A quantity of the silver salt is decided by taking into account a target amount of the silver colloid particles and a percentage of the silver salt reduced by the reducing agent. In case of the silver nitrate, about 15 to 70 parts by weight of the silver nitrate is used on the basis of 100 parts by weight of the aqueous silver salt solution.

The aqueous silver salt solution is prepared by dissolving the silver salt in pure water and is gradually dropped into the aqueous solution in which the dispersant and the reducing agent are dissolved.

As described above, in this step, the Ag⁺ ions contained in the silver salt is reduced by the reducing agent so that the Ag⁺ ions are transformed into silver atoms to produce the silver particles in the aqueous solution. At this time, the dispersant is adsorbed to the surfaces of the silver particles to form silver colloid particles.

This produces an aqueous solution (aqueous dispersion solution) in which the silver colloid particles are dispersed in a colloidal form, that is, the colloid solution.

In addition to the silver colloid particles, the residual reducing agent and the dispersant are likely to exist in the thus obtained colloid solution as ions. Thus, an ion concentration of the colloid solution as a whole becomes high.

In the colloid solution of this state, the silver particles are aggregated to produce aggregates and the aggregates are easily precipitated. For this reason, it is preferred that cleaning is performed to remove superfluous ions of the residual reducing agent and dispersant present in the colloid solution and to reduce the ion concentration thereof.

Examples of cleaning methods include: a method of repeating several times the steps of leaving the colloid solution containing the silver colloid particles at rest for a specified time, removing supernatant liquid thus created, adding pure water to the colloid solution, stirring the colloid solution, leaving the colloid solution at rest for a specified time and removing supernatant liquid thus created; a method of performing centrifugal separation in place of leaving the colloid solution at rest; a method of removing ions by ultrafiltration; and the like.

Further, the following method may be used. In this method, first, after the colloid solution is produced, the pH thereof is adjusted to an acidic area of 5 or lower so that the above reaction equation (1) is shifted to the right side, thereby positively aggregating the silver colloid particles (metal colloid particles) due to reduction of the electrical repulsion forces of the surfaces of the silver particles. Next, in this aggregated state of the silver colloid particles, salts and the solvent are removed from the colloid solution.

In this regard, in the case where a sulfur compound having a low molecular weight such as the mercapto acid is used as the dispersant, such a sulfur compound forms stable bonds to the surfaces of the silver particles (metal particles) to produce the silver colloid particles (metal colloid particles).

Therefore, by adjusting the pH of the colloid solution to an alkaline area of 6 or higher once again, the aggregated silver colloid particles are re-dispersed therein with ease. In this way, it is possible to obtain a colloid solution having excellent dispersion stability.

In the method of producing the ink 10 of this embodiment, it is preferred that, at the end of the above step, the pH of the colloid solution, in which the silver colloid particles are dispersed, is finally adjusted to 6 through 11 by adding, if necessary, an aqueous alkali metal hydroxide solution to the colloid solution.

Due to the cleaning performed after reduction, a concentration of sodium ions as electrolytic ions is sometimes decreased. With the colloid solution of this state, equilibrium of a reaction represented by the following reaction equation (2) is shifted to the right side.

—COO⁻Na⁺+H₂O→—COOH+Na⁺+OH⁻  (2)

In this case, the silver colloid particles exhibit a decrease in its electrical repulsion force and they (that is, the silver particles) suffer from reduction in its dispersibility. For this reason, the equilibrium of the reaction equation (2) is shifted to the left side and the silver colloid particles are stabilized by adding an appropriate amount of alkali metal hydroxide.

The alkali metal hydroxide used at this time includes, e.g., the same compound as used in first adjusting the pH of the above aqueous solution. If the pH is lower than 6, the equilibrium of the reaction equation (2) is shifted to the right side, consequently making the silver colloid particles unstable.

In contrast, if the pH is higher than 11, precipitation of hydroxide salt of residual ions such as iron ions is apt to occur, which is undesirable. In the case where the iron ions or the like are removed in advance, no big problem is posed even when the pH is higher than 11.

It is preferred that positive ions such as sodium ions are added in the form of hydroxide. This makes it possible to use self-protolysis of water. Therefore, this is the most effective way of adding the positive ions such as sodium ions to the colloid solution.

Next, the above other components as well as the sugar alcohol B and the like as described above are added to the colloid solution produced in this way, to thereby obtain a conductive pattern formation ink (the ink 10 of the present invention).

Conductive Pattern

Next, a description will be made on the conductive pattern of this embodiment. The conductive pattern of this embodiment is a thin-film type conductive pattern formed by supplying the ink 10 on a ceramics compact (including a pre-member which will be transformed into the ceramics compact) by using the ink jet apparatus 50 as described above and heating it so that the silver particles can be bonded together.

At least on a surface of the conductive pattern, the silver particles are bonded to one another without leaving any gap therebetween.

Especially, since this conductive pattern is formed using the ink 10 as described above, it is possible to prevent disconnections of the formed conductive pattern due to ejecting failure of the ink 10, contact between the adjacent conductive patterns, and the like. Further, since the conductive pattern becomes homogeneous, it is possible to obtain a conductive pattern having a higher reliability.

The conductive pattern of this embodiment is formed by supplying the ink 10 on the ceramics compact (including the pre-member thereof) using a droplet ejection method to obtain the pre-pattern, drying the pre-pattern (ink), that is, removing the water-based dispersion medium from the pre-pattern, and then sintering the same.

A drying temperature is preferably at the range of 40 to 100° C. and more preferably at the range of 50 to 70° C. This makes it possible to more effectively prevent generation of cracks when the pre-pattern (ink) has been dried. The sintering step is preferably performed by heating the dried pre-pattern (ink) at 160° C. or more for 20 minutes or more.

In this regard, it is to be noted that the sintering step of the pre-pattern can be carried out simultaneously with debinding the sugar alcohol B, the surfactant B and the polyglycerin compound and sintering the ceramics compact.

The specific resistance of the conductive pattern is preferably smaller than 20 μΩcm and more preferably 15 μΩcm or less. The term “specific resistance” used herein refers to specific resistance available when the ink 10 is supplied to the ceramics compact, heated at 160° C. and dried.

If the specific resistance is equal to or greater than 20 μΩcm, it is difficult to use the conductive pattern in a conductivity-requiring application, e.g., in an electrode formed on a circuit substrate.

When forming the conductive pattern of this embodiment, it is possible to provide a thick conductive pattern by repeatedly performing the steps of supplying the ink 10 by the afore-mentioned supplying method, preliminarily heating the ink 10 to evaporate the water-based dispersion medium such as water or the like, and supplying once again the ink 10 on the preliminarily heated film.

The polyglycerin compound and the silver colloid particles are left (remain) in the ink 10 from which the water-based dispersion medium such as water or the like has been evaporated. For this reason, there is no possibility that the pre-pattern thus formed by the ink 10 may be washed away (diffused) even when it is not fully dried. Therefore, it becomes possible to apply the ink 10 once again after the ink 10 is first applied, dried and left at rest for a long period of time.

Furthermore, since the polyglycerin compound as described above is a compound having chemical and physical stabilities, there is also no possibility that the ink 10 constituting the pre-pattern may undergo a change in quality even when the ink 10 is applied, dried and left at rest for a long period of time. It also becomes possible to supply the ink 10 once again, which makes it possible to form the pre-pattern with a uniform quality.

This eliminates possibility that the conductive pattern may become a multi-layer structure, which would lead to an increase in inter-layer specific resistance and, eventually, an increase in specific resistance of the conductive pattern as a whole.

By going through the above-noted steps, the conductive pattern of this embodiment can be formed thicker than a conductive pattern produced by a conventional ink. More specifically, it is possible to form a conductive pattern whose thickness is equal to or greater than 5 μm.

Since the conductive pattern of this embodiment is formed by the afore-mentioned ink 10, cracks are seldom generated even when the conductive pattern is formed into a thickness of 5 μm or more. This makes it possible to construct a conductive pattern with reduced specific resistance.

There is no need to particularly restrict an upper limit of the thickness of the conductive pattern. However, if the thickness of the conductive pattern is too great, difficulties may be encountered in removing the water-based dispersion medium and the polyglycerin compound, which may possibly increase the specific resistance of the conductive pattern. For this reason, it is preferred that the conductive pattern has a thickness of about 100 μm or less.

The conductive pattern of this embodiment exhibits good adhesion with respect to the base member (substrate) set forth above.

In this regard, it is to be noted that the conductive pattern described above can be used in high-frequency modules, interposers, micro-electromechanical systems, acceleration sensors, acoustic surface wave devices, antennas, odd-shaped electrodes (including comb electrodes) of mobile communication equipments such as a cellular phone, a PDA or the like, and electronic components of various kinds of measuring instruments.

Wiring Substrate and Method of Producing Wiring Substrate

Next, a description will be made on one example of a wiring substrate (ceramic circuit substrate) having the conductive pattern formed by the ink 10 of the present invention and one example of a method of producing the wiring substrate.

The wiring substrate of the present embodiment constitutes an electronic component used in various kinds of electronic equipments. The wiring substrate is produced by forming a circuit pattern which consists of various kinds of wirings, electrodes and the like, a laminated ceramic condenser, a laminated inductor, an LC filter and a composite high-frequency component on a substrate.

FIG. 3 is a longitudinal section view showing one example of the wiring substrate according to the present invention, that is, a ceramic circuit substrate. FIG. 4 is an explanatory view schematically illustrating the steps of a method of producing the wiring substrate shown in FIG. 3, that is, the ceramic circuit substrate.

FIGS. 5A and 5B are views for explaining a production process of the wiring substrate shown in FIG. 3, that is, the ceramic circuit substrate. FIG. 1 is a perspective view showing a schematic configuration of the ink jet apparatus (droplet ejection apparatus). FIG. 2 is a pattern diagram for explaining a schematic configuration of the ink jet head (droplet ejection head).

As shown in FIG. 3, the ceramic circuit substrate (wiring substrate) 1 includes a laminated substrate 3, which is formed by laminating a plurality of (e.g., about ten through twenty) ceramic substrates 2, and a circuit 4 formed on one outermost layer, i.e., one end surface, of the laminated substrate 3, the circuit 4 being made of fine wirings and the like.

The laminated substrate 3 includes a plurality of circuits (conductive patterns) 5 formed by the ink 10 of the present invention and arranged between the ceramic substrates 2.

Contacts (vias) 6 that make contact with circuits 5 are formed in the circuits 5. With this configuration, the circuits 5 arranged one above another are conducted through the contacts 6. Just like the circuits 5, the circuit 4 is formed by the ink 10 of the present invention.

Next, a method of producing the ceramic circuit substrate 1 will be described with reference to the schematic process view illustrated in FIG. 4.

Prepared first as raw powder are ceramic powder constituted of alumina (Al₂O₃) and titanium oxide (TiO₂) each having an average particle size of the range of about 1 to 2 μm and glass powder constituted of boron silicate glass having an average particle size of the range of about 1 to 2 μm.

The ceramic powder and the glass powder are mixed with each other in an appropriate mixing ratio, e.g., in a weight ratio of 1:1 to obtain a mixed powder.

Next, slurry is obtained by adding a suitable binder, a plasticizer, an organic solvent (dispersant) and the like to the mixed powder, and then mixing and stirring the same. In this regard, it is to be noted that polyvinyl butyral is preferably used as the binder. The polyvinyl butyral is water-insoluble and is apt to be dissolved or swollen in what is called an oil-based organic solvent.

Then, the slurry thus obtained is coated on a PET film in a sheet shape using a doctor blade, a reverse coater or the like. Depending on production conditions of an article, the slurry is formed into a sheet having a thickness of several micrometers to several hundred micrometers, and then the sheet is wound into a roll.

Subsequently, the roll is severed in conformity with use of the article and is cut into a sheet having a specified size. In this embodiment, the roll is cut into, e.g., a square sheet whose one side has a length of 200 mm to obtain a sheet-like ceramic molded body (that is, a ceramic green sheet) 7.

If necessary, through-holes are formed in given positions by punching (processing) the ceramic green sheet 7 with a CO₂ laser, a YAG laser, a mechanical punch or the like. A thick-film conductive paste in which metal particles are dispersed is filled into the through-holes to form portions which will be transformed into the contacts 6.

Further, portions which will be transformed into terminal portions (not shown) are formed in the given positions of the ceramic green sheet 7 by screen printing the thick-film conductive paste. In this way, the ceramic green sheet 7, on which the portions which will be transformed into the contacts 6 and terminal portions are formed, is obtained.

In this regard, it is to be noted that the ink 10 of the present invention can be used as the thick-film conductive paste.

Next, a pre-pattern 11 which will be transformed into the circuits 5 (corresponding to the conductive pattern of the present invention) is formed on one surface of the ceramic green sheet 7 in such a state that the pre-pattern 11 continuously extends from the portions which will be transformed into the contacts 6.

In other words, as illustrated in FIG. 5A, the ink 10 described above is supplied on the ceramic green sheet 7 by using the ink jet apparatus 50 as shown in FIG. 1, thereby forming the pre-pattern 11 to become the circuits (conductive pattern) 5.

At least a part of the water-based dispersion medium is evaporated from a surface side of the ink 10 shot against the ceramic green sheet 7 in forming the pre-pattern 11. At this time, evaporation of the water-based dispersion medium is accelerated, since the ceramic green sheet 7 is heated by a rubber heater which is provided on a lower surface of the table 46 of the ink jet apparatus 50 shown in FIG. 1.

The ink 10 shot against the ceramic green sheet 7 is thickened first in a peripheral edge of the surface thereof. That is to say, the peripheral edge of the surface of the ink 10 begins to be thickened because an amount (concentration) of solid contents (silver colloid particles) in the peripheral portion becomes higher than in the central portion more rapidly.

The peripheral edge portion of the ink 10 thus thickened stops its spreading action along a plane direction of the ceramic green sheet 7. This makes it easy to control a shot diameter and hence a line width.

A heating temperature of the ceramic green sheet 7 is set equal to the drying conditions mentioned earlier.

Once the pre-pattern 11 is formed in the above manner, the same steps are repeated to form a required number of, e.g., about ten to twenty, ceramic green sheets 7 each having the pre-pattern 11.

Then, the PET film is peeled off from the ceramic green sheets 7 and a laminated body 12 is obtained by laminating the ceramic green sheets 7 as illustrated in FIG. 4. At this time, the ceramic green sheets 7 are arranged so that, if necessary, the pre-patterns 11 of the ceramic green sheets 7 laminated one above another can be connected through the portions which will be transformed into the contacts 6.

Thereafter, the laminated ceramic green sheets 7 are heated at a temperature which is a glass transition temperature or higher of a binder constituting the ceramic green sheet 7. Then, the laminated ceramic green sheets 7 are pressed and each of the laminated ceramic green sheets 7 is bonded each other to obtain the laminated body 12.

The laminated body 12 thus formed is heated by use of, e.g., a belt type furnace. As a result, the ceramic substrate 2 (wiring substrate of the present invention) is obtained by sintering the respective ceramic green sheets 7 as shown in FIG. 5B.

As the silver colloid particles forming the pre-patterns 11, including the silver particles (metal particles), are sintered, the pre-patterns 11 are transformed into the circuits (conductive patterns) 5 consisting of a wiring pattern or an electrode pattern. Further, at this time, the portions are also transformed into the contacts 6 and the terminal portions, respectively.

In this way, by subjecting the laminated body 12 to the heat treatment as mentioned above, the laminated body 12 is transformed into the laminated substrate 3 shown in FIG. 3.

In this regard, a heating temperature of the laminated body 12 is preferably equal to or more than a softening point of the glass component (glass powder) contained in the ceramic green sheets 7. More specifically, it is preferred that the heating temperature is in the range of 600 to 900° C.

Heating conditions are selected to make sure that the temperature is elevated and dropped at a suitable speed. Furthermore, the laminated body 12 is maintained for a suitable period of time at a maximum heating temperature, i.e., at the temperature of the range of 600 to 900° C.

The glass component (glass powder) of the ceramic substrates 2 thus obtained can be softened by elevating the heating temperature up to a temperature above the softening point of the glass component, i.e., the temperature range noted above.

Therefore, if the laminated body 12 is subsequently cooled down to a normal temperature so that the glass component can be hardened, the respective ceramic substrates 2 that constitute the laminated substrate 3 are firmly bonded to the circuit (conductive pattern) 5.

The ceramic substrates 2 obtained by heating the laminated body 12 up to the temperature range noted above become what is called low temperature co-fired ceramic (LTCC) which means the ceramic fired at a temperature of 900° C. or less.

Here, the silver particles (metal particles) present in the ink 10 delivered on the ceramic green sheet 7 are fused and continuously joined to one another, thereby exhibiting conductivity.

By the heat treatment noted above, the circuits 5 are formed to make direct contact with and come into connection with the contacts 6 of the ceramic substrates 2. In a hypothetical case that the circuits 5 are merely placed on the ceramic substrates 2, no mechanical connection strength would be secured between the circuits 5 and the ceramic substrates 2. Therefore, the circuits 5 may possibly destroyed by shocks or the like.

In this embodiment, however, the circuits 5 are firmly fixed to the ceramic substrates 2 by first softening and then hardening the glass component contained in the ceramic green sheet 7. As a result, the formed circuits 5 can have high mechanical strength.

Using such a heat treatment, the circuit 4 can be formed simultaneously with the circuits 5, thereby producing the ceramic circuit substrate 1.

While certain preferred embodiments of the present invention have been described hereinabove, the present invention is not limited thereto. The filling liquid may be used as a washing liquid for washing a droplet ejection apparatus, in particular a reservoir and ink chambers formed in a droplet ejection head of the droplet ejection apparatus.

Further, although the colloid solution is used in the foregoing embodiments as the dispersion solution prepared by dispersing the metal particles in the water-based dispersion medium, the dispersion solution may not be the colloid solution.

Furthermore, although it has been described that the silver colloid particles including the silver particles are dispersed in the ink (colloid solution) in embodiments described above, the colloid particles may include metal particles other than the silver particles.

Examples of a metal constituting the other metal particles include copper, palladium, platinum, gold, alloy thereof, and the like. These metals may be used singly or in combination of two or more of them.

In case of using metal particles constituting of the alloy, the alloy may contain the above mentioned metal as its major component, and other metals. Further, it may also be possible to use alloy obtained by mixing the above mentioned metals with each other in an arbitrary ratio. Mixed particles (e.g., combination of silver particles, copper particles and palladium particles mixed in an arbitrary ratio) may be dispersed in the ink (colloid solution).

The above mentioned metals are low in resistivity and are stable such that they are not oxidized by a heat treatment. Therefore, use of these metals makes it possible to form a conductive pattern that exhibits low resistance and high stability.

Furthermore, although it has been described that the ceramic substrate and the conductive pattern are formed by supplying the ink to the ceramics compact (ceramic green sheet) and sintering it in embodiments described above, a substrate (compact) other than the ceramic substrate or ceramics compact may be used.

Such a substrate used for forming the conductive pattern is not particularly limited to a specific substrate. Examples of the substrate include a ceramic sintered body, an alumina sintered body, a polyimide resin, a phenol resin, a glass epoxy resin, a glass and the like. Further, the conductive pattern may be obtained by directly supplying the ink to the ceramic substrate.

EXAMPLES

Hereinafter, the present invention will be described in more detail by virtue of examples. However, the present invention is not limited to these examples.

[1] Preparation of Filling Liquid and Conductive Pattern Formation Ink

In each of Examples and Comparative Examples, a conductive pattern formation ink (ink) and a filling liquid were produced as follows.

Example 1

Preparation of Filling Liquid

An ion-exchange water, xylitol as a sugar alcohol A, and OLFINE EXP4036 (produced by Nissin Chemical Industry Co., Ltd., which contains 80 wt % of an acetylene glycol-based compound having a bilateral symmetry structure in which the acetylene group is placed at the center) as a surfactant A were mixed in amounts thereof shown in FIG. 1 to obtain a filling liquid.

Preparation of Conductive Pattern Formation Ink

17 g of trisodium citrate dihydrate and 0.36 g of tannic acid were dissolved in 50 mL of water alkalified by adding 3 mL of an aqueous 10N NaOH solution thereto, to obtain an aqueous solution. 3 mL of a 3.87 mol/L aqueous silver nitrate solution was added to the aqueous solution thus obtained drop by drop.

A silver colloid solution was obtained by stirring the above aqueous solution for two hours. The silver colloid solution thus obtained was dialyzed until conductivity thereof was decreased to 30 μS/cm or less, thereby desalting the silver colloid solution.

At the end of dialysis, coarse silver colloid particles were removed from the silver colloid solution by performing centrifugal separation at 3000 rpm for 10 minutes.

Thereafter, xylitol as a sugar alcohol B, polyglycerin a having a weight-average molecular weight of 500, and SURFYNOL 104PG-50 and OLFINE EXP4036 (produced by Nissin Chemical Industry Co., Ltd.) as a surfactant B were added to the silver colloid solution in which the coarse silver colloid particles were removed.

In this case, when a pH of the silver colloid solution did not fall within the range of 6 to 11, the pH of the silver colloid solution was adjusted so as to fall within the range of 6 to 11 by using a NaOH aqueous of 1 N. Further, ion-exchange water for adjusting a concentration of the silver colloid solution was added therein to obtain an ink. In this regard, it is to be noted that an amount of each of the components of the ink is shown in FIG. 2.

Example 2

A filling liquid and an ink were prepared in the same manner as the Example 1 except that sorbitol was used as the sugar alcohol A and the sugar alcohol B.

Example 3

A filling liquid and an ink were prepared in the same manner as the Example 1 except that both xylitol and sorbitol were used as the sugar alcohol A and the sugar alcohol B.

Example 4

A filling liquid and an ink were prepared in the same manner as the Example 1 except that both xylitol and lactitol were used as the sugar alcohol A and the sugar alcohol B.

Example 5

A filling liquid and an ink were prepared in the same manner as the Example 1 except that both sorbitol and maltitol were used as the sugar alcohol A and the sugar alcohol B.

Example 6

A filling liquid and an ink were prepared in the same manner as the Example 1 except that both sorbitol and lactitol were used as the sugar alcohol A and the sugar alcohol B.

Examples 7 to 9

In each of the Examples 7 to 9, a filling liquid and an ink were prepared in the same manner as the Example 1 except that an amount of the sugar alcohol A was changed as shown in FIG. 1.

Examples 10 to 12

In each of the Examples 10 to 12, a filling liquid and an ink were prepared in the same manner as the Example 1 except that an amount of the surfactant A was changed as shown in FIG. 1.

Examples 13 to 15

In each of the Examples 13 to 15, a filling liquid and an ink were prepared in the same manner as the Example 3 except that an amount of the surfactant A was changed as shown in FIG. 1.

Example 16

A filling liquid and an ink were prepared in the same manner as the Example 1 except that the OLFINE EXP4036 as the surfactant A was changed to OLFINE EXP4001 (produced by Nissin Chemical Industry Co., Ltd., which contains 80 wt % of an acetylene glycol-based compound having a bilateral symmetry structure in which the acetylene group is placed at the center).

Examples 17 to 19

In each of the Examples 17 to 19, a filling liquid and an ink were prepared in the same manner as the Example 1 except that the OLFINE EXP4036 as the surfactant A was changed to SURFYNOL 104PG-50 (produced by Nissin Chemical Industry Co., Ltd., which contains 50 wt % of an acetylene glycol-based compound having a bilateral symmetry structure in which the acetylene group is placed at the center), and an amount thereof was changed as shown in FIG. 1.

Example 20

A filling liquid and an ink were prepared in the same manner as the Example 1 except that the filling liquid was prepared as follows.

Preparation of Filling Liquid

An ion-exchange water, xylitol as a sugar alcohol A, OLFINE EXP4036 (produced by Nissin Chemical Industry Co., Ltd., which contains 80 wt % of an acetylene glycol-based compound having a bilateral symmetry structure in which the acetylene group is placed at the center) as a surfactant A, and trisodium citrate dihydrate were mixed in amounts thereof shown in FIG. 1 to obtain a filling liquid.

Example 21

A filling liquid and an ink were prepared in the same manner as the Example 20 except that trisodium citrate dihydrate was changed to mercaptoacetic acid.

Example 22

A filling liquid and an ink were prepared in the same manner as the Example 1 except that the ink was prepared as follows.

3.0 g of mercaptoacetic acid as a sulfur compound having a low molecular weight was added to 1000 mL of a 50 mmol/L aqueous silver nitrate solution with being stirred, and then 26 wt % ammonia water was added to the aqueous silver nitrate solution to adjust pH thereof to 10.0.

Next, 50 mL of a 400 mmol/L aqueous sodium borohydride solution as a reducing agent was rapidly added to the aqueous silver nitrate solution under room temperature so that a reduction reaction was generated, to thereby produce silver colloid particles in which the mercaptoacetic acid was adsorbed to surfaces of silver particles in the aqueous silver nitrate solution. In this way, a colloid solution was obtained.

Thereafter, a 20 wt % aqueous nitric acid solution was added to the colloid solution so that the pH thereof was adjusted to 3.0, to precipitate the silver colloid particles in the colloid solution, the precipitated silver colloid particles were filtrated by a vacuum filter, and then they were washed until conductivity of a filtrate was decreased to 10.0 μS/cm or less, to thereby obtain a wet cake constituted of the silver colloid particles.

The wet cake constituted of the silver colloid particles was added to water so that an amount thereof contained in the water became 10 wt %, and then 26 wt % ammonia water was added to the water with being stirred to adjust the pH thereof to 9.0. In this way, the silver colloid particles were re-dispersed in the water, and then the water was concentrated to thereby obtain a silver colloid solution.

Thereafter, the ink was prepared in the same manner as the Example 1.

Comparative Example 1

A filling liquid and an ink were prepared in the same manner as the Example 1 except that the sugar alcohol A was not used in the preparing process of the filling liquid.

Comparative Example 2

A filling liquid and an ink were prepared in the same manner as the Example 1 except that the surfactant A was not used in the preparing process of the filling liquid.

A composition of the filling liquid in each of the Examples 1 to 22 and the Comparative Examples 1 and 2 was shown in FIG. 1. Further, a composition of the ink in each of the Examples 1 to 22 and the Comparative Examples 1 and 2 was shown in FIG. 2.

In this regard, it is to be noted that “XY” means xylitol, “SB” means sorbitol, “ML” means maltitol, and “RA” means lactitol in each of the FIG. 1 and FIG. 2. Further, it is also to be noted that “4036” means OLFINE EXP4036, “4001” means OLFINE EXP4001, and “104” means SURFYNOL 104PG-50 in each of the FIG. 1 and FIG. 2.

Furthermore, viscosities and surface tensions of the filling liquid and the ink obtained in each of the Examples 1 to 22 and the Comparative Examples 1 and 2 were shown in each of the FIG. 1 and FIG. 2. In this regard, it is to be noted that the viscosities are measured according to JIS Z8809 using a vibration type viscometer at a temperature of 25° C., and the surface tensions are measured according to JIS K3362 at a temperature 25° C.

TABLE 1 Filling Liquid Composition of filling liquid Sugar alcohol A Surfactant A Other components Ion-exchange Surface Amount Amount Amount Amount water Viscosity tension Kind [wt %] kind [wt %] kind [wt %] HLB kind [wt %] [wt %] [mPa · s] [dyn/cm] Ex. 1 XY 6 — — 4036 1 13 — — 93 0.8 22.7 Ex. 2 SB 6 — — 4036 1 13 — — 93 0.9 22.4 Ex. 3 XY 6 ML 1 4036 1 13 — — 92 0.8 21.8 Ex. 4 XY 6 RA 1 4036 1 13 — — 92 0.7 21.5 Ex. 5 SB 6 ML 1 4036 1 13 — — 92 1.0 22.4 Ex. 6 SB 6 RA 1 4036 1 13 — — 92 1.0 22.5 Ex. 7 XY 3 — — 4036 1 13 — — 96 0.7 22.9 Ex. 8 XY 15 — — 4036 1 13 — — 84 1.1 22.8 Ex. 9 XY 25 — — 4036 1 13 — — 74 1.2 23.2 Ex. 10 XY 6 — — 4036 0.02 13 — — 93.98 0.8 29.1 Ex. 11 XY 6 — — 4036 0.1 13 — — 93.9 0.8 25.8 Ex. 12 XY 6 — — 4036 0.5 13 — — 93.5 0.8 23.0 Ex. 13 XY 6 ML 1 4036 0.02 13 — — 92.98 0.9 28.7 Ex. 14 XY 6 ML 1 4036 0.1 13 — — 92.9 0.8 26.0 Ex. 15 XY 6 ML 1 4036 0.5 13 — — 92.5 0.9 23.5 Ex. 16 XY 6 — — 4001 1 9 — — 93 1.0 21.7 Ex. 17 XY 6 — — 104 1 4 — — 93 0.9 33.5 Ex. 18 XY 6 — — 104 0.02 4 — — 93.98 0.7 49.1 Ex. 19 XY 6 — — 104 0.05 4 — — 93.9 0.9 38.8 Ex. 20 XY 6 — — 4036 1 13 Sodium citrate 1 92 0.9 22.3 Ex. 21 XY 6 — — 4036 1 13 Mercaptoacetic 1 92 1.1 23.1 acid Ex. 22 XY 6 — — 4036 1 13 — — 93 0.7 22.5 Comp. — — — — 4036 1 13 — — 99 0.6 23.1 Ex. 1 Comp. XY 6 — — — — — — — 94 0.8 57.3 Ex. 2

TABLE 2 Conductive pattern formation ink Composition of conductive pattern formation ink Amount of silver SURFYNOL OLFINE colloid Sugar alcohol B (Surfactant B) (Surfactant B) particles Amount Amount Amount Amount [wt %] Kind [wt %] kind [wt %] kind [wt %] HLB kind [wt %] HLB Ex. 1 40 XY 6 — — 104 0.02 4 4036 0.006 13 Ex. 2 40 SB 6 — — 104 0.02 4 4036 0.006 13 Ex. 3 40 XY 6 ML 1 104 0.02 4 4036 0.006 13 Ex. 4 40 XY 6 RA 1 104 0.02 4 4036 0.006 13 Ex. 5 40 SB 6 ML 1 104 0.02 4 4036 0.006 13 Ex. 6 40 SB 6 RA 1 104 0.02 4 4036 0.006 13 Ex. 7 40 XY 6 — — 104 0.02 4 4036 0.006 13 Ex. 8 40 XY 6 — — 104 0.02 4 4036 0.006 13 Ex. 9 40 XY 6 — — 104 0.02 4 4036 0.006 13 Ex. 10 40 XY 6 — — 104 0.02 4 4036 0.006 13 Ex. 11 40 XY 6 — — 104 0.02 4 4036 0.006 13 Ex. 12 40 XY 6 — — 104 0.02 4 4036 0.006 13 Ex. 13 40 XY 6 ML 1 104 0.02 4 4036 0.006 13 Ex. 14 40 XY 6 ML 1 104 0.02 4 4036 0.006 13 Ex. 15 40 XY 6 ML 1 104 0.02 4 4036 0.006 13 Ex. 16 40 XY 6 — — 104 0.02 4 4036 0.006 13 Ex. 17 40 XY 6 — — 104 0.02 4 4036 0.006 13 Ex. 18 40 XY 6 — — 104 0.02 4 4036 0.006 13 Ex. 19 40 XY 6 — — 104 0.02 4 4036 0.006 13 Ex. 20 40 XY 6 — — 104 0.02 4 4036 0.006 13 Ex. 21 40 XY 6 — — 104 0.02 4 4036 0.006 13 Ex. 22 40 XY 6 — — 104 0.02 4 4036 0.006 13 Comp. 40 XY 6 — — 104 0.02 4 4036 0.006 13 Ex. 1 Comp. 40 XY 6 — — 104 0.02 4 4036 0.006 13 Ex. 2 Conductive pattern formation ink Composition of conductive pattern formation ink Polyglycerin Ion- Compound exchange Surface Amount water Viscosity tension kind [wt %] [wt %] [mPa · s] [dyn/cm] Ex. 1 Polyglycerin 9 44.974 6.1 36.2 Ex. 2 Polyglycerin 9 44.974 6.7 35.6 Ex. 3 Polyglycerin 9 43.974 5.9 35.8 Ex. 4 Polyglycerin 9 43.974 5.5 35.5 Ex. 5 Polyglycerin 9 43.974 6.8 35.9 Ex. 6 Polyglycerin 9 43.974 7.1 35.3 Ex. 7 Polyglycerin 9 44.974 6.1 36.2 Ex. 8 Polyglycerin 9 44.974 6.1 36.2 Ex. 9 Polyglycerin 9 44.974 6.1 36.2 Ex. 10 Polyglycerin 9 44.974 6.2 36.0 Ex. 11 Polyglycerin 9 44.974 6.2 36.5 Ex. 12 Polyglycerin 9 44.974 6.1 35.1 Ex. 13 Polyglycerin 9 43.974 7.3 35.9 Ex. 14 Polyglycerin 9 43.974 7.1 36.2 Ex. 15 Polyglycerin 9 43.974 7.5 36.1 Ex. 16 Polyglycerin 9 44.974 5.9 36.7 Ex. 17 Polyglycerin 9 44.974 6.0 35.2 Ex. 18 Polyglycerin 9 44.974 6.1 36.2 Ex. 19 Polyglycerin 9 44.974 6.1 36.2 Ex. 20 Polyglycerin 9 44.974 5.9 36.1 Ex. 21 Polyglycerin 9 44.974 6.3 35.5 Ex. 22 Polyglycerin 9 44.974 6.2 35.9 Comp. Polyglycerin 9 44.974 6.1 36.7 Ex. 1 Comp. Polyglycerin 9 44.974 6.1 36.3 Ex. 2

Evaluation 1 of Replacing Filling Liquid with Ink

The filling liquid obtained in each of the Examples 1 to 22 and the Comparative Examples 1 and 2 was filled into an ink flow path (ink chambers and ink reservoir) formed in an ink jet head as shown in FIG. 2 which was included in an ink jet apparatus as shown in FIG. 1. Then, the ink jet head was left in a clean room of a class 100 for 24 hours under the conditions of a temperature of 25° C. and a relative humidity of 50%.

Next, the ink jet apparatus as shown in FIG. 1 was produced by using the ink jet head as shown in FIG. 2. Thereafter, the filling liquid filled into the ink flow path of the ink jet head was discharged.

After the filling liquid was discharged, the ink jet head was left for 5 minutes. Then, the ink obtained in each of the Examples 1 to 22 and Comparative Examples 1 and 2 was filled into the ink flow path of the ink jet head. Thereafter, 10,000 droplets of the ink were continuously ejected from nozzles of the ink jet head to a sheet.

A total amount of the ink ejected from each of the nozzles of the ink jet head was obtained. Then, an average ejection amount of the ink in each of the nozzles was calculated by using the total amount of the ink ejected from each of the nozzles and 10,000 droplets. Thereafter, an absolute ΔW (ng) of a difference between the average ejection amount and a target ejection amount W_(T) (ng) of the ink was calculated in each of the nozzles of the ink jet head.

And then, a ratio (ΔW/W_(T)) between the ΔW and the target ejection amount W_(T) (ng) was obtained. The ratio was evaluated according to the following four criteria A to D described below. If a value of the ratio (ΔW/W_(T)) was small, it was evaluated that the ink was stably ejected from the nozzle of the ink jet head.

That is to say, there are no defects such as incorporation of air bubbles to the ink flow path, mix of air bubbles to the ink or the like so that the ink was reliably filled into the ink flow path.

A: A value of the ratio (ΔW/W_(T)) is lower than 0.020.

B: A value of the ratio (ΔW/W_(T)) is 0.020 or higher but lower than 0.420.

C: A value of the ratio (ΔW/W_(T)) is 0.420 or higher but lower than 0.720.

B: A value of the ratio (ΔW/W_(T)) is 0.720 or higher.

Evaluation 2 of Replacing Filling Liquid with Ink

The filling liquid obtained in each of the Examples 1 to 22 and the Comparative Examples 1 and 2 was filled into an ink flow path (ink chambers and ink reservoir) formed in an ink jet head as shown in FIG. 2 which was included in an ink jet apparatus as shown in FIG. 1. Then, the ink jet head was left in a clean room of a class 100 for 24 hours under the conditions of a temperature of 25° C. and a relative humidity of 50%.

Next, the ink jet apparatus as shown in FIG. 1 was produced by using the ink jet head as shown in FIG. 2. Thereafter, the ink was again filled into the ink flow path formed in the ink jet head included in the ink jet apparatus while discharging the filling liquid therefrom by the ink. The filling process was carried out by flowing the ink for 300 seconds at a flow rate of 1.0 ml/min.

Thereafter, 10,000 droplets of the ink were continuously ejected from nozzles of the ink jet head to a sheet. A total amount of the ink ejected from each of the nozzles of the ink jet head was obtained. Then, an average ejection amount of the ink in each of the nozzles was calculated by using the total amount of the ink ejected from each of the nozzles and 10,000 droplets.

Thereafter, an absolute ΔW (ng) of a difference between the average ejection amount and a target ejection amount W_(T) (ng) of the ink was calculated in each of the nozzles of the ink jet head.

And then, a ratio (ΔW/W_(T)) between the ΔW and the target ejection amount W_(T) (ng) was obtained. The ratio was evaluated according to the following four criteria A to D described below. If a value of the ratio (ΔW/W_(T)) was small, it was evaluated that the ink was stably ejected from the nozzle of the ink jet head.

That is to say, there are no defects such as aggregates of the silver particles in the ink or the like so that the ink was reliably filled into the ink flow path.

A: A value of the ratio (ΔW/W_(T)) is lower than 0.020.

B: A value of the ratio (ΔW/W_(T)) is 0.020 or higher but lower than 0.420.

C: A value of the ratio (ΔW/W_(T)) is 0.420 or higher but lower than 0.720.

B: A value of the ratio (ΔW/W_(T)) is 0.720 or higher.

These results are shown in Table 3.

TABLE 3 Evaluation 1 of Evaluation 2 of replacing filling replacing filling liquid with ink liquid with ink Ex. 1 A A Ex. 2 A A Ex. 3 A A Ex. 4 A A Ex. 5 A A Ex. 6 A A Ex. 7 C B Ex. 8 A A Ex. 9 A A Ex. 10 C B Ex. 11 B B Ex. 12 A B Ex. 13 C B Ex. 14 B B Ex. 15 A B Ex. 16 A A Ex. 17 C B Ex. 18 C C Ex. 19 B C Ex. 20 A A Ex. 21 A A Ex. 22 A A Comp. D C Ex. 1 Comp. D D Ex. 2

As shown in Table 3, the filling liquid according to the present invention, that is, the filling liquids obtained in Examples 1 to 22 could be replaced with the ink in the ink flow path easily, reliably and stably. In contrast, the filling liquids obtained in Comparative Examples 1 and 2 could not be obtained satisfying results. 

1. In a droplet ejection apparatus for forming a conductive pattern with a conductive pattern formation ink comprised of a water-based dispersion medium and metal particles dispersed in the water-based dispersion medium by an ink jet method, the droplet ejection apparatus including a droplet ejection head having a reservoir with ink chambers for storing the conductive pattern formation ink and a plurality of nozzles from which droplets of the conductive pattern formation ink are to be ejected by the ink jet method, wherein a filling liquid is used instead of the conductive pattern formation ink for filling the reservoir and the ink chambers to prevent the reservoir and the ink chambers from being dried when the droplet ejection apparatus is not used for a certain period of time, wherein the filing liquid is comprised of the water-based dispersion medium, a sugar alcohol A and a surfactant A.
 2. The filling liquid as claimed in claim 1, wherein the conductive pattern formation ink further comprises a sugar alcohol B, wherein the sugar alcohol A contained in the filling liquid includes the same kind of sugar alcohol as a kind of the sugar alcohol B contained in the conductive pattern formation ink.
 3. The filling liquid as claimed in claim 1, wherein the conductive pattern formation ink further comprises a surfactant B, and the surfactant B is constituted of components, wherein the surfactant A contained in the filling liquid includes at least a part of the components constituting the surfactant B contained in the conductive pattern formation ink.
 4. The filling liquid as claimed in claim 1, wherein the sugar alcohol A includes at least one of xylitol and sorbitol.
 5. The filling liquid as claimed in claim 1, wherein an amount of the sugar alcohol A contained in the filling liquid is in the range of 3 to 25 wt %.
 6. The filling liquid as claimed in claim 1, wherein a hydrophile lipophile balance (HLB) of the surfactant A is in the range of 8 to
 16. 7. The filling liquid as claimed in claim 1, wherein the surfactant A includes an acetylene glycol-based compound.
 8. The filling liquid as claimed in claim 7, wherein the acetylene glycol-based compound has an acetylene group, and a bilateral symmetry structure in which the acetylene group is placed at the center.
 9. The filling liquid as claimed in claim 1, wherein an amount of the surfactant A contained in the filling liquid is in the range of 0.05 to 5 wt %.
 10. The filling liquid as claimed in claim 1 further comprising hydroxyl acid or a salt of the hydroxyl acid having three or more COOH and OH groups in total, wherein a number of the COOH groups is equal to or greater than a number of the OH group(s).
 11. The filling liquid as claimed in claim 1 further comprising mercapto acid or a salt of the mercapto acid having two or more COOH and SH groups in total.
 12. The filling liquid as claimed in claim 1, wherein surface tension of the filling liquid is in the range of 20 to 50 dyn/cm, wherein the surface tension of the filling liquid is equal to or smaller than surface tension of the conductive pattern formation ink. 